PRIMATES (Lat. primus, first), the name given by Linnaeus to the highest order of mammals (see Mammalia), which was taken by him to include not only man, apes, monkeys and lemurs, but likewise bats. The latter group is now separated as a distinct order (see Chiroptera). It has also been proposed to remove from the Primates the lemurs, constituting the group Prosimiae, or Lemuroidea, to form an order by themselves; but general opinion is now against this view, and they are accordingly here regarded as representing a sub-order of Primates, all the other members of which are included in a second subordinal group—the Anthropoidea, or Simiae. Support to the view that lemurs should be included in the order is afforded by the discovery in Madagascar of an extinct species (Nesoithecus) presenting certain characters connecting it with monkeys on the one hand and with lemurs on the other.
In this broader sense the Primates may briefly be defined
as follows. All the members of the order are plantigrade
mammals, normally with five fingers and five toes, which are
generally armed with broad flattened nails, although these are
rarely replaced on single digits, or on all the digits, by claws or
claw-like nails. The dental formula is i.22, c.11, d.22 (33); m.33 (22);
all the teeth in advance of the molars being normally preceded
by milk-teeth. The molars are three-, four- or five-cusped,
but the cusps may in some cases coalesce into transverse
ridges. The thumb and great toe are, as a rule, opposable
to the other digits. The clavicles (collar-bones) are complete;
there is nearly always a free centrale bone in the wrist, or
carpus, in which the scaphoid and lunar are likewise generally
separate. The orbits (and the eyes) are directed more or less
Fig. 1.—Lateral and lower views of
the Skull of a Langur Monkey
(Semnopithecus), to show the forward direction
and complete closure of the orbits,
and the characters of the dentition of
the Old World Catarhini.
forwards, and generally
surrounded by bone (fig. 1),
while the lower jaw has
a vertical movement on
the upper. With a few
exceptions the stomach is
simple; and a duodenojejunal
flexure of the intestine
and a caecum are
present. The diet is generally
vegetable, but may be
mixed, or, rare1y, consisting
of insects. The uterus may
be either bicornuate or
simple; and the placenta
either discoidal and
deciduate, or diffuse and
non-deciduate, with a great
development of the allantois.
The clitoris may or
may not be perforate; the
penis is pendent; and the
testes are extra-abdominal,
situate either in a scrotum
behind the penis or in a
similarly situated fold of
the integument. At most
the teats are four in
number, but generally only
two situated on the breast,
although occasionally
abdominal or even inguinal.
As a rule only a single
offspring is produced at a
birth, such offspring being
always born in a completely helpless condition.
With the exception of man, who has adapted himself to exist in all climates, the Primates are essentially a tropical and subtropical group, although some of the monkeys inhabit districts where the winter climate is severe. The great majority—in fact nearly all—of the members of the order are arboreal in their habits. In size there is great variation, the extremes in this respect being represented by man and the gorilla on the one side, and the marmosets and tarsiers, which are no larger than squirrels, on the other.
As regards the proper meaning of the popular names “monkey,” “baboon” and “ape,” it appears that these are in the main general terms which, with the exception of the second, may be applied indifferently to all the members of the first sub-order. “Baboon” appears to be properly applicable to the dog-faced African species, and may therefore be conveniently restricted to the members of the genus Papio and their immediate relatives. “Ape,” on the other hand, may be specially used for the tailless man-like representatives of the order; while the term “monkey” may be employed for all the rest, other than lemurs; monkeys being, however, divisible into sub-groups, such as macaques, langurs, guerezas, mangabeys, &c. This usage cannot, however, be universally employed, and the term “monkeys” may be employed for the entire group.
Anthropoidea.—The Primates, as already mentioned, are divisible into two main groups, or sub-orders, of which the first includes man, apes, baboons and monkeys. For this group Professor Max Weber employs the name Simiae (in contradistinction to Prosimiae for the lemurs). Since, however, to take as the title for a group which includes man himself the designation of creatures so much lower in the scale is likely to be repugnant, it seems preferable to employ the designation Anthropoidea for the higher division of the order.
As the essential features distinguishing the Anthropoidea from the second sub-order may best be indicated under the heading of the latter, reference may at once be made to some of the more striking characters of the members of the former group. The proportions of the body as regards the relative lengths of the two pairs of limbs to one another and to that of the trunk vary considerably. Both pairs may be much elongated, as in Ateles and Hylobates, and either sub-equally, as in the first of these, or with the arms greatly in excess, as in the second. The legs may be excessively short, and the arms, at the same time, excessively long, as in the orang-utan. Both pairs may be short and sub-equal, as in many of the baboons (Papio). Only in Nyctipithecus and the Hapalidae does the excess in length of the lower limbs over the upper exceed or equal that which is found in man. The length of the tail presents some noteworthy points. It is found at its greatest absolute length, and also greatly developed relatively, being about twice the length of the trunk, in such monkeys as the Indian langurs; but its greatest relative length is attained in the spider-monkeys (Ateles), where it reaches three times the length of the trunk. The constancy of the degree of its development varies much in different groups. In the greater number of genera it is long in all the species, and in some (Simia, Anthropopithecus and Hylobates) it is absent in all. In others it may be long or short, or completely absent, as in macaques (Macacus).
The form of the head presents great differences—it may be rounded, as in Ateles; produced vertically, as in Simia; drawn out posteriorly to an extreme degree, as in Chrysothrix; or anteriorly, as in the baboons. A production of the muzzle, necessitated by the presence of large teeth, exists in the chimpanzee (Anthropopithecus), but in the baboons, not only is this prolongation carried farther, but the terminal position of the nostrils gives a dog-like aspect to the face.
The eyes may be small compared with the size of the head, as in the baboons; but they may, on the contrary, attain a relatively, enormous size, as in Nyctipithecus. They are always forwardly directed, and never much more separated one from another than in man; they may, however, be more closely approximated, as in the squirrel-monkeys (Chrysothrix) of South America.
The ears are always well developed, and very generally have their postero-superior angle pointed. They ma be large and small in the same genus, as in Anthropopithecus (chimpanzee and gorilla); but only in the gorilla do we find, even in a rudimentary condition, that soft depending portion of the human ear termed the “lobule.” The nose has scarcely ever more than a slight prominence, and yet an enormous development is to be met with in the proboscis-monkey (Nasalis); while in the snub-nosed monkeys (Rhinopithecus) we find a sharply prominent, though smaller and extremely upturned nose. The hoolock gibbon also possesses a prominent but slightly aquiline nose. The terminal position of the nostrils in the baboons has already been mentioned. These apertures may be closely approximated, as in all the man-like apes (Simiidae and Hylobatidae), or they may be separated one from the other by a broad septum, as in the Cebidae, its breadth, however, varying somewhat in different genera, as in Ateles and Eriodes, and Callithrix and Nyctipithecus. The lips are generally thin, but may be very extensile, as in the orang-utan.
The hands are generally provided with thumbs, though these organs (as in the African guerezas, Colobus, and the American spider-monkeys, Ateles) may be represented only by small nailless tubercles. The thumb is more human in its proportions in the chimpanzee than in any other of the higher apes. As compared with the length of the hand, it is most man-like in the lowest American monkeys, such as Chrysothrix and Hapale. In spite of greater relative length it may, however, little merit the name of thumb, as it is but slightly opposable to the other digits in any of the American monkeys, and is not at all so in the Hapalidae. The “great toe” is never rudimentary and, except in man, in place of being the longest digit of the foot, is constantly the shortest. As compared with the entire length of the foot, it is most man-like in the chimpanzee and some gibbons, and smallest of all in the orang-utan, and next smallest in Hapale. Every digit is provided with a nail, except the great toe of the orang-utan and the rudimentary tubercle representing the thumb in Ateles and Colobus. The nail of the great toe is flat in every species, but the other nails are never so flat as are the nails of man. The lateral compression of the nails becomes more strongly marked in some Cebidae, e.g. Eriodes, but attains its extreme in the Hapalidae, where every nail, except that of the great toe, assumes the form of a long, curved and sharply pointed claw.
With the single exception of man, the body is almost entirely clothed with copious hair, and never has the back naked. In the gibbons, the langurs, the macaques and the baboons, naked spaces (ischiatic callosities) are present on that part of the body which is the main support in the sitting posture. These naked spaces are subject to swelling at the season of sexual excitement. Such naked spaces are never found in any of the American monkeys. No ape or monkey has so exclusive and preponderating a development of hair on the head and face as exists in man. As to the head, long hair is found thereon in Hapale oedipus and in some of the langurs and guerezas, whilst certain macaques, like the Chinese bonnet-monkey (Macacus sinicus), have the hair of the head long and radiating in all directions from a central point on the crown. A beard is developed in the male orang-utan; and the Diana monkey (Cercopithecus diana) has long hair on the cheeks and chin. The wanderoo (Macacus silenus) has the face encircled by a kind of mane of long hairs; and many of the marmosets have a long tuft of hairs on each side of the head. American monkeys exhibit some extremes respecting hair-development. Thus in some of the howlers (as in some of the guerezas of the Old World) the hair of the flanks is greatly elongated. Some also have an elongated beard, but the latter structure attains its maximum of development in the couxio (Pithecia satanas). Some of the species of the American genus Pithecia have the hair of the body and tail very long, others have the head of the female furnished with elongated hair; while the allied Uacaria calva has the head bald. Long hair may be developed from the shoulders as in Papio hamadryas and Theropithecus gelada. Very long hair is also developed on the back of the snub-nosed monkeys (Rhinopithecus) in winter. The direction of the hair may sometimes vary in nearly allied forms, the hairs on the arm and fore-arm respectively being often so directed that the tips converge towards the elbow. Such is the case in most of the higher apes, yet in Hylobates agilis all the hair of both these segments is directed towards the wrist. The hair presents generally no remarkable character as to its structure. It may, however, be silky, as in Hapale rosalia, or assume the character of wool, as in the woolly spider-monkeys (Eriodes) and Macacus tibetanus, which inhabits Tibet.
Fig. 2.—Skeleton of Chacma Baboon (Papio porcarius), showing the great relative length of the facial part of the Skull.
Great brilliance of colour is sometimes found in the naked parts of the body, particularly in the baboons and some of the other Cercopithecidae, and especially in the regions of the face and sexual organs. Among these latter rose, turquoise-blue, green, golden-yellow and vermilion appear, in various combinations, in one or other or both of these regions, and become especially brilliant at the period of sexual excitement.
The skeleton, more especially in the higher forms, is in the main similar to that of man, so that only a brief notice is necessary. In the skull considerable variation in regard to the proportionate length of the face to that of the brain-case (cranial portion) exists in the two sexes, owing to the general development of large tusks in the males (other than in man, who is not now under consideration). Generally speaking, the elongation of the facial portion, as compared to the cranial, increases as we pass from the higher to the lower forms. The increase does not, however, occur regularly, being greater in the orang-utan and chimpanzee than in some of the langurs (Semnopithecus, fig. 1); the maximum development of this feature occurs in the dog-faced baboons (Papio, fig. 2). In American monkeys, with the exception of the howlers (Alouata, fig. 3), the facial part is relatively smaller than in Old World monkeys and apes; while in the squirrel-monkeys (Chrysothrix) it is even smaller than in man himself. In none of the Old World group does the forehead present that rounded and elevated contour characteristic of man, although the height of this region is great in the orang-utan (fig. 4). Curiously enough, American monkeys, especially those included in Pithecia, are the most man-like in this respect. The skull of the male gorilla is characterized by the great development of the crests for muscular attachment, one of these (superciliary) overhanging the orbits, a second (sagittal) traversing the middle line of the upper surface, while a third (lambdoid) forms an inverted V on the occiput, and affords attachment for the muscles of the neck. In the gorilla the orbits are much as in man, but in the orang-utan they are more rounded. They become very large in Hylobates, but attain an enormous size in the American Nyctipithecus. The extent to which each orbit opens into the adjacent temporal fossa, i.e. the size and shape of the sphenomaxillary fissure, varies considerably; this is narrow and much elongated in the gorilla and the baboons, but short in the langurs and spider-monkeys. It is most closed in the howlers, where it sometimes all but disappears entirely. The mastoid process never attains the large relative size it has in man; but it is prominent in the baboons and larger macaques, as well as in the chimpanzee and gorilla, its development bearing relation to the size and weight of the head. As the mastoid diminishes, the under surface of the petrosal assumes a swollen or bladder-like condition.
Fig. 3.—Skull and Hyoid-bone of a Howler-Monkey (Alouata). In nature the hyoid-bone, which is bladder-like, is placed between the two branches of the lower jaw.
The plane of the foramen magnum, as compared with the basicranial axis, varies with the projection of the occiput; it generally forms a less open angle with that axis than in man, but in Chrysothrix the angle is yet more open than in the human skull. The cheek, or zygomatic, arches bend outwards and upwards in the gorilla and some baboons, but decrease in relative as well as absolute size in the smaller forms—notably in Chrysothrix. No long slender styloid process is normally attached to the skull, though such may be the case in the baboons. An external bony auditory meatus (or tube) is present in Old World but absent in New World monkeys. In all apes and monkeys the premaxillae have a distinctness of development and a relative size not found in man; the sutures separating them from the maxillae remaining visible, except in the chimpanzee, after the adult dentition has been attained. The maxillae develop great swollen tuberosities in the baboons and the black ape of Celebes. Thee nasal bones are small, and generally flatter than in man; being in the orang-utan quite flat. They are convex in some langurs and all baboons; but the proboscis-monkey has its nasals no more developed than those of other species. The nasals seem to attain their maximum of relative size in the howlers. The lower jaw, or mandible, is always in one piece in adults; and is most man-like in the siamang, which alone has a slight chin. On the other hand, in other gibbons the angle is produced downwards and backwards, as also in marmosets. Its maximum of relative size is attained in the howlers (fig. 3), where the broad ascending part serves to protect and shelter the enormously developed body of the hyoid. Air-cells may be developed, as in the gorilla, in the parts adjacent to the mastoid. Frontal sinuses are generally absent in the Old World group, being replaced by coarse cellular bone. In old age the sutures of the skull become obliterated, the one between the two nasals disappearing at an early age in Old World monkeys. In the spider-monkeys and howlers the tentorium, or membrane dividing the hemispheres of the brain from the cerebellum, becomes bony.
Fig. 4.—Skull of adult male Orang-utan (Simia satyrus).
The spinal column of apes and monkeys always lacks the S-like curvature of that of man, the nearest approach to this occurring in the baboons (fig. 2). The number of dorsal vertebrae varies from eleven in some species of Cercopithecus and Macacus to fourteen in certain gibbons or fifteen in the American night-apes (Nyctipithecus). In the American Cebidae the number seldom falls below thirteen; in the orang-utan it is twelve, as in man, but thirteen in the chimpanzee and gorilla. In most cases the dorsal and lumbar regions are about equal in length, but the lumbar region is the shorter in the man-like group, and less than half the length of the dorsal in the gorilla. The lumbar spinous processes are vertical, or project backwards in the man-like apes, gibbons and spider-monkeys; in the others they project forwards, especially in Cebidae. The lumbar transverse processes project outwards, more or less at right angles to the axis of the spine, or else forwards. The sacrum attains its greatest absolute length in the gorilla, but is relatively longer than in man in all the man-like group. Hylobates has the relatively longest sacrum. The number of vertebrae included in the sacrum varies more or less with age; with the exception of the Simiidae and Hylobatidae, there are generally only two or three; but in Ateles, Hylobates, and Uacaria there may be four; while in the Simiidae there are always five, and sometimes six. In most apes the sacrum and lumbar vertebrae lie in one slightly curved line, the gorilla and chimpanzee presenting in this respect a great contrast to the human structure. In the orang-utan the sacro-vertebral angle is rather more marked; but in some baboons it is so much so as almost to rival that of man.
Fig. 5.—Skeleton of South American Spider-Monkey (Ateles), to illustrate the length of the limbs and tail, and the slenderness of the former.
With the exception of the man-like apes and gibbons and the Barbary ape (Macacus inuus), the caudal vertebrae of monkeys exceed four in number; but the mandril, Papio (Maimon) maimon, has sometimes only five. The short-tailed macaques and uakaris have from about fifteen to seventeen, the shortness of the tail being occasioned rather by a diminution in the size of the component vertebrae than by a decrease in number. In the other forms the number varies between twenty and thirty-three, the latter being the number attained in the spider-monkeys (fig. 5). The proportion borne by this region of the spine to the more anterior parts is greatest in the spider monkeys of the genus Ateles, almost three to one; in the other longest-tailed genera it is rarely so large as two to one. The absolute length of the tail is greatest in the langurs and guerezas, where also the individual caudal vertebrae attain their greatest length, namely two inches. The caudal vertebrae generally increase in length from the sacrum till about the seventh, eighth or ninth, which, with the tenth and eleventh, are the longest in most long-tailed forms. In Ateles the eleventh, twelfth, thirteenth and fourteenth vertebrae are the longest. In most members of the sub-order the breast bone or sternum is narrow, and consists of a more or less enlarged upper portion, or manubrium, followed by a chain of sub-equal elongated bones from three to six in number. In man, man-like apes and gibbons there is, however, a broad sternum; or one consisting of a manubrium, followed by one bone only, as in Hylobates. In the orang-utan the breast-bone long remains made up of ossifications arranged in pairs, side by side, successively. The true ribs are seven in number on each side in the highest forms, but in Hylobates there are sometimes eight; in Ateles there are sometimes nine pairs; in Hapale the number varies from six to eight, and from seven to eight in the other genera. The “angles” of the ribs are never so marked as in man; most so in Hylobates. Pithecia is distinguished by the greater relative breadth of the ribs. In no ape or monkey is the thorax half as broad again as it is deep from back to breast. Nevertheless, in the Simiidae and Hylobatidae, its transverse diameter exceeds its depth by from about one-fourth to a little under one-third of the latter. In Ateles (and sometimes also in Alouata) the thorax is wider than deep, but in the rest it is deeper than wide.
The greatest absolute length of the fore-limb occurs in the gorilla
(fig. 6) and the orang-utan. The humerus never has a perforation
Fig. 6.—Skeleton of the
Gorilla (Anthropopithecus
gorilla), to exhibit the flattened
sternum, the broad and shallow
thorax, and the great length of
the fore-limbs.
(entepicondylar) on the inner side
of its lower extremity. Except in
the man-like apes, the ulna articulates
with the wrist (carpus). The
hand is capable of pronation and
supination on the fore-arm; and
except in man, the chimpanzee and
the gorilla there is a centrale in the
carpus. The phalanges are the same
in number in apes and monkeys
as in man, except that in Ateles
and Colobus the thumb may have
but one small nodular phalange or
none. The phalanges are generally
more curved than in man, and,
except in the Hapalidae, the
terminal ones are flattened from
back to front. In the Hapalidae
they are laterally compressed,
curved, and pointed to support the
claws characteristic of that family.
The length of the thumb with its
metacarpal bears a much greater
proportion to that of the spine in
Hylobates and Simia than in man.
With the exception of Ateles and
Colobus, the shortest thumb, thus
estimated, is found in Nyctipithecus
and Chrysothrix.
The hind-limb, measured from the summit of the femur to the tip of the longest digit, is absolutely greatest in the gorilla, and then in the orang-utan and the chimpanzee. If the foot be removed, the leg of the chimpanzee is longer than that of the orang-utan. The ankle, or tarsus, consists of the same seven bones as in man, and these bones are so arranged, or bound together by ligaments, as to form a transverse and an antero-posterior arch. In no ape or monkey, however, do the lower ends of the inner metatarsals form the anterior point of support of the antero-posterior arch, as in man. The calcaneum, except in the gorilla, is shorter compared with the spine than in man. The phalanges of the foot are the same in number as in man, except that the great toe of the orang-utan has often but one. They are very like their representatives in the hand, and are convex above, concave and flattened below. Only in the Hapalidae are the terminal phalanges laterally compressed instead of flattened. The toes are never nearly so short relatively in apes and monkeys as in man; yet the proportion borne by the great toe, with its metatarsal, to the spine closely approximates in the gorilla to the proportion existing in man, and this proportion is exceeded in Hylobates and Ateles.
Omitting all reference to the muscles, we find that in apes and monkeys the absolute size of the brain never approaches that of man; the cranial capacity being never less than 55 cub. in. in any normal human subject, while in the orang-utan and chimpanzee it is but 26 and 27½ cub. in. respectively. The relative size of the brain varies inversely with the size of the whole body, as is the case in warm-blooded vertebrates generally. The hemispheres of the brain are almost always so much developed as to cover over the cerebellum, the only exceptions being the howlers and the siamang (Hylobates syndactylus). In the latter the cerebellum is slightly uncovered, but it is considerably so in the former. In Chrysothrix the posterior lobes are more largely developed relatively than in man. As in mammals generally, much convoluted hemispheres are correlated with a considerable absolute bulk of body. Thus in Hapale (and here only) we find the hemispheres quite smooth, the only groove being that which represents the Sylvian fissure. In Simia and Anthropopithecus, on the contrary, they are richly convoluted. A hippocampus minor is present in all apes and monkeys, and in some Cebidae is larger relatively than in man, and absolutely larger than the hippocampus major. Of all apes and monkeys the orang-utan has a brain most like that of man; indeed it may be said to be like man's in all respects save that it is much inferior in size and weight, and that the hemispheres are more symmetrically convoluted and less complicated by minor foldings. The human brain, as known by European specimens, has been supposed to differ from that of apes and monkeys by the absence of the so-called simian fold (Affenspalte) on the posterior portion of the main hemispheres. On studying a large series of Egyptian and Sudani brains, Professor G. Elliot Smith finds, however, that this simian fold, or sulcus, can be distinctly recognized. “It is easy,” he writes, “to select examples from the series of Egyptian and Sudanese brains in my possession, in which the pattern formed by the occipital sulci on the lateral surface of the hemisphere in individual anthropoid apes is so exactly reproduced that the identity of every sulcus is placed beyond reasonable doubt. . . . And if we take individual examples of gorilla-brains, it becomes still easier to match the occipital pattern of each of them to numerous human brains. . . . It is easy to appreciate the difficulties which have beset investigators of European types of brain, and to understand the reasons for the common belief in the absence of the supposed distinctly simian sulci in the lateral aspect of the occipital region of the human brain.”
In no ape or monkey does the series of teeth form so perfect an arch as in man, the opposite series of cheek-teeth tending to become more parallel. None has the teeth placed in one uninterrupted series in each jaw, as is the case in the human species; but there is always a small gap between the upper canine and the adjacent incisor, and between the lower canine and the adjacent premolar. This condition is due to the excessive size of the canines, the interspaces giving passage to the tips of these teeth. This prolongation of the canines into tusk-like weapons of offence and defence (especially developed in the males) makes a great difference between the aspect of the dentition in apes and man. The number of the teeth is the same as in man in all Old World Primates. The New World Cebidae have an additional premolar on each side of each jaw, while the Hapalidae have a molar the less. The incisors are nearly vertical, save in Pithecia and its allies, where their tips project forward. The canines are considerably longer than the incisors, except in Hapale, where the lower incisors equal them in length. The premolars differ structurally from the molars much as in man, except that the first lower one may be modified in shape to give passage to the upper canine, as in the baboons. The grinding surface of the molars consists generally of two incomplete transverse ridges, the end of each ridge projecting more than the intermediate part, indicating the position of the four original tubercles. In the man-like apes there is, however, in the upper molars a ridge running obliquely from the front inner tubercle, or cusp, outwards and backwards to the hind outer tubercle. In the Cercopithecidae this ridge is wanting, but it reappears in Ateles and Alouata amongst the Cebidae. In the Hapalidae the tubercles of the molars are more produced and sharp-pointed, in harmony with the insectivorous habits of the marmosets. The last lower molar may be reduced or much enlarged as compared with the others. Thus in Cercopithecus talapoin it has but three tubercles, while in the macaques and baboons it is very large, and has five well-developed cusps. The number of milk-teeth is as in man, except that American monkeys have an additional one. In general the canines are the last teeth to be cut of the permanent dentition, their cutting sometimes causing such constitutional disturbance as to produce convulsions and death. In the gibbons, however, the canines accompany, if they do not precede, the appearance of the hindmost molar, while in the orang-utan they at least sometimes make their appearance before the latter.
The stomach is simple in all apes and monkeys except langurs, guerezas, and their allies. It is especially human in shape in Hylobates, except that the pylorus is somewhat more elongated and distinct. It is of a rounded form in Pithecia, and in Hapale the cardiac orifice is exceptionally near the pylorus. In the langur group it is sacculated, especially at the cardiac end, being, in fact, very like a colon spirally coiled. The intestine is devoid of valvulae conniventes, but provided with a well-developed caecum, which is, however, short and conical in the baboons. Only in the man-like apes is there a vermiform appendix. The colon may be much longer relatively than in man, as in the man-like apes; it may be greatly sacculated, as in Hylobates; or devoid of sacculations, as in Cebus. The liver may be very like man's, especially in gibbons, the orangutan, and the chimpanzee; but in the gorilla both the right and left lobes are cleft by a fissure almost as much as in the baboons. In the langur group the liver is much divided, and placed obliquely to accommodate the sacculated stomach. The lateral lobes in Hapale are much larger than the central lobe. The caudate lobe is very large in Cebidae, especially in Ateles, and above all in Pithecia. There is always a gall-bladder.
The larynx in many members of the sub-order is furnished with sac-like appendages, varying in different species as regards number, size and situation. They may be dilatations of the laryngeal ventricle (opening into the larynx below the false vocal chords), as in the man-like apes; or the may open above the false vocal chords so as to be extensions of the thyro-hyoid membrane, as in gibbons. There may be but a single median opening in the front part of that membrane at the base of the epiglottis, as in Cercopithecidae, or there may be a single median opening at the back of the trachea, just below the cricoid cartilage, as in spider-monkeys; and while there is in some instances only a single sac, in other instances, as in the howlers, there may be five. These may be enormous, meeting in the middle line in front, and extending down to the axillae, as in the gorilla and orang-utan. Finally a sac may occupy the cavity of the expanded body of the hyoid-bone, as in howlers (fig. 3). The hyoid has its basilar part generally somewhat more convex and enlarged than in man; but in howlers it becomes greatly enlarged and deeply excavated, so as to form a great bony bladder-like structure (fig. 3). The cornua of the hyoid are never entirely absent, but the anterior or lesser cornua may be so, as in the howlers. The anterior cornua never exceed the posterior cornua in length; but they may be (Cercopithecus) more developed relatively than in man, and may even be jointed, as in Lagothrix.
|
| (From a sketch by Wolf from life.) |
Fig. 7.—An Immature Chimpanzee (Anthropopithecus troglodytes).
The lungs are generally similar to those of man, although, as in gibbons, the right one may be four-lobed. In the man-like apes the great arteries are likewise of the human type; but in the Hylobatidae and Cercopithecidae the left carotid may arise from the innominate. The discoidal and deciduate placenta is generally two-lobed, although single in the howlers; in the marmosets it is unusually thick. American monkeys differ from their Old World cousins in having two umbilical veins in place of a single one. In the Cercopithecidae gestation lasts about seven months, but in the marmosets is reduced to three. The young, which are generally carried on the breast, are suckled for about six months in most monkeys.
Man-like Apes.—-In common with man, the apes and monkeys of the Old World form a section—Catarrhina—of the sub-order Anthropoidea, characterized by the following features: There are only two pairs of premolar teeth, so that the complete dental formula is i. 22, c. 11, p. 22, m. 33. The tympanum has an external bony tube, or meatus; but there is no tympanic bulla. A squamoso-frontal suture causes the frontal and the alisphenoid bones to enter largely into the formation of the orbital plate; and the orbito-temporal foramen is small. Cheek-pouches and callosities on the buttocks are frequently present. The nails are flat or rounded, the descending colon of the intestine has an S-like (sigmoid) flexure; the caecum is simple, and there may be a vermiform appendix. The inter-nasal septum is thin, and the nostrils are directed outwards. The tail, which may be rudimentary, is never prehensile. The ethmoturbinal bones of the nasal chamber are typically united. Laryngeal sacs are commonly developed. In addition to the primary discoidal placenta, a secondary, and sometimes temporary one is developed.
Fig. 8.—Adult Male Gorilla (Anthropopithecus gorilla).
It does not come within the province of this article to treat of man (see Anthropology); but it may be mentioned that the distinctive characteristics of the family Hominidae (including the single genus Homo), as compared with those of the Simiidae, or man-like apes, are chiefly relative. These are shown by the greater size of the brain and brain-case as compared with the facial portion of the skull, smaller development of the canine teeth of the males, more complete adaptation of the structure of the vertebral column to the vertical position, greater length of the lower as compared with the upper extremities, and the greater length of the great toe, with almost complete absence of the power of bringing it in opposition to the other four toes. The last and the small size of the canine teeth are perhaps the most marked and easily defined distinctions that can be drawn between the two groups, so far as purely zoological characters are concerned. The regular arch formed by the series of teeth is, however, as already mentioned, another feature distinguishing man from the man-like apes.
In common with the gibbons (Hylobatidae) the man-like apes, or Simiidae, are distinguished from the lower representatives of the present sub-order by the following features: The sternum is short and broad, and the thorax wide and shallow (fig. 6), while the pelvis, as shown in the same figure, is more or less laterally expanded, and hollow on its inner-surface; and the number of dorso-lumbar vertebrae ranges from sixteen to eighteen. The arm is longer than the leg; and while the hair on the fore-arm is directed upwards, that of the upper-arm slopes downwards to meet it at the elbow. Cheek-pouches are absent. The cusps of the molars are separate; and five in number above and four below. The caecum has a vermiform appendix; and the secondary placenta merely forms a temporary fold. The Simiidae are specially characterized by the absence of callosities on the buttocks; the presence of sixteen or seventeen dorso-lumbar vertebrae, and of twelve or thirteen pairs of ribs; the wrinkling of the enamel of the cheek-teeth; the great expansion and concavity of the iliac bones of the pelvis; and the application of only the edge of the sole of the foot to the ground in walking.
The existing members of the family are referable to at least two genera, the one African and the other Asiatic. The first genus, Anthropopithecus,[1] is typified by the West African chimpanzee, A. troglodytes (fig. 7), and is characterized by the absence of excessive elevation in the skull, by the fore limb not reaching more than half-way down the shin, the presence of thirteen pairs of ribs, the well-developed great toe, the absence of a centrale in the carpus, and the black or grey hair. There is a well-developed laryngeal sinus, which may extend downwards to the axilla. Chimpanzees are characterized by the large size of the ears, and typically by the small development of the supra-orbital ridges. The latter are, however, more developed in the Central African A. tchego (of which the kulu-kamba is a local phase); this form—whether regarded as a species or a race—being thus more gorilla-like (see Chimpanzee).
The gorilla (Anthropopithecus gorilla, fig. 8), of which there are likewise several local forms, ranging from the West Coast through the forest-tract to East Central Africa, and apparently best regarded as sub-species, is frequently made the type of a second genus—Gorilla; but is extremely close to the chimpanzee, from which it is perhaps best distinguished by its much smaller ears. It is the largest of the apes, although the females are greatly inferior in stature and bulk to the males. The gorilla is also a much less completely arboreal ape than the chimpanzee, in consequence of which more of the sole of the foot is applied to the ground in walking. The enormous supra-orbital ridges of the skull of the male, and likewise the large and powerful tuslis in that sex are very characteristic. A full-grown gorilla will stand considerably over six feet in height. According to Dr A. Keith, in addition to its smaller and flatter ears, the gorilla may be best distinguished from the chimpanzee by the presence of a nasal fold running to the margin of the upper lip; by the large size and peculiar characters of the tusks and cheek-teeth; by its broad, short, thick hands and feet, of which the fingers and toes are partially webbed; by the long heel; and by the relative length of the upper half of the arm as compared with the fore-arm. An important distinctive feature of the skull of the gorilla is the great length of the nasal bones. Finally, in adult life the gorilla is sharply differentiated from the chimpanzee by its sullen, unnameable, ferocious disposition.
As regards the relationship existing between the gorilla and the chimpanzee, Dr Keith observes: “An examination of all the structural systems of the African anthropoids leads to the inference that the gorilla is the more primitive of the two forms, and approaches the common parent stock more nearly than does the chimpanzee. The teeth of the gorilla, individually and collectively, form a complete dentition, a dentition at the very highest point of development; the teeth of the chimpanzee show marked signs of retrogression in development both in size and structure. The muscular development and the consequent bony crests for muscular attachment of the gorilla far surpass those of the chimpanzee. The muscular development of the adult chimpanzee represents that of the adolescent gorilla. Some of the bodily organs of the gorilla belong to a simpler and earlier type than those of the chimpanzee. But in one point the chimpanzee evidently represents more nearly the parent form—its limbs and body are more adapted for arboreal locomotion; of the two, the gorilla shows the nearer approach to the human mode of locomotion. On the whole the evidence at our disposal points to the conclusion that the chimpanzee is a derivative from the gorilla stock, in which, with a progressive brain development, there have been retrograde changes in most of the other parts of the body. The various races of chimpanzee differ according to the degree to which these changes have been carried.” (See Gorilla.)
From both the chimpanzee and the gorilla the orang-utan, or mias (Simia satyrus), of Borneo and Sumatra is broadly distinguished by the extreme elevation of the skull (fig. 4), the excessive length of the fore limbs, which reach to the ankle, the presence of only twelve pairs of ribs and of a centrale in the carpus, the short and rudimentary great toe, and the bright-red colour of the hair. Adult males are furnished with a longish beard on the chin, and they may also develop a large warty prominence, consisting of fibro-cellular tissue, on each side of the face, which thus assumes an extraordinary wide and flattened form. There is no vestige of a tail. The hands are very long; but the thumb is short, not reaching the end of the metacarpal bone of the index-finger. The feet have exceedingly long toes, except the great toe, which only reaches to the middle of the first joint of the adjacent toe, and is often destitute not only of a nail, but of the second phalange also. It nevertheless possesses an opponens muscle. The brain has the hemispheres greatly convoluted, and is altogether more like the brain of man than is that of any other ape. A prolongation is developed from each ventricle of the larynx, and these processes in the adult become enormous, uniting together in front over the windpipe and forming one great sac which extends down between the muscles to the axilla. The canine teeth of adult males are very large. In Borneo the orang-utan displays great variability, and has accordingly been divided into a number of local races, in some of which the males apparently lack the lateral expansion of the face. Whether the Sumatran orang-utan should be regarded as a distinct species, with two local races, may be left an open question. (See Orang-Utan).
Gibbons.—The comparatively small, long-armed and tailless Asiatic apes known as gibbons have been very generally included in the same family as the man-like apes; but since they differ in several important features—to say nothing of their smaller bodily size—it has recently been proposed to refer them to a family apart, the Hylobatidae. The distinctive features of this family include the presence of small naked callosities on the buttocks, the possession of eighteen dorso-lumbar vertebrae and thirteen pairs of ribs, the absence of foldings in the enamel of the molar teeth, the slight lateral expansion and concavity of the iliac bones of the pelvis, and the application of the whole sole of the foot to the ground in walking. The vertebral column presents no trace of the sigmoid flexure which is developed partially in the Simiidae and completely in the Hominidae. None of the gibbons have any rudiment of a tail; and the canines are elongated and tusk-like. When the body is erect, the arms are so long that they reach the ground. The great toe is well developed, reaching to the middle or end of the first joint of the adjacent toe; but the thumb only attains to, or reaches a little beyond, the upper end of the first joint of the index-finger. There is a centrale in the carpus. The laryngeal sacs are no longer prolongations of the laryngeal ventricles, but open into the larynx above the false vocal chords. The group is distributed throughout the forest-regions of south-eastern Asia, eastwards and southwards from Assam, and is represented by a considerable number of species. Among these, the siamang, Hylobates syndactylus, of Sumatra and the Malay Peninsula, differs from all the rest by the union of the index and third fingers up to the base of their terminal joints, in consequence of which this species is regarded as representing a sub-genus (Symphalangus) by itself, while all the others belong to Hylobates proper. The general colour of gibbons is either pale fawn or black, with or without a white band across the forehead. In a female from Hainan in the menagerie of the Zoological Society of London, the colour of the coat changed from black to fawn about the time full maturity was attained. Apparently no such change takes place in the male. According to Dr W. Volz, the two banks of the Lematang River in the Palembang district of Sumatra are respectively inhabited by two different species of gibbons—on the west bank is found the siamang (Hylabates syndactylus), while the country to the east of the river is the home of the agile gibbon, or waw-waw (H. agilis). It is not necessary to capture, or even to see, specimens of the two species in order to satisfy oneself as to their limitations, for they may be readily distinguished by their cries: the siamang calling in a single note, whereas the cry of the waw-waw forms two notes. The remarkable thing about their distribution in Palembang is that the two species are found in company throughout the rest of Sumatra; and even in Palembang itself they inhabit the mountain districts, where the river is so narrow that they could easily leap over it, and yet they keep to the opposite banks. Gibbons are perhaps the most agile of all the Old World monkeys, rivalling in this respect the American spider-monkeys, despite their lack of the prehensile tails of the latter (see Gibbon).
Langur Group.—The well-known long-tailed langur monkeys of India and the adjacent regions are the first representatives of the third family of apes and monkeys, which includes all the remaining members of the sub-order now under consideration. In the Cercopithecidae, as the family is called, the following features are distinctive: The sternum, or breast-bone, is narrow and elongated, and the thorax compressed and wedge-shaped, while the iliac bones of the pelvis are narrow, with the inner surface flat; the dorso-lumbar vertebrae are nineteen or twenty in number. The front limbs are shorter than the hind pair; the whole sole of the foot is applied to the ground in walking; and the hair on the arm is directed downwards from the shoulder to the hand. There are always bare callosities on the buttocks, and very generally cheek-pouches. The caecum is conical. Transverse ridges connect the cusps of the molars. The secondary placenta is fully developed.
The first group of the family is represented by the langurs and their allies, collectively forming the sub-family Semnopithecinae, in which the tail and hind limbs are very long, and the body is slender; there are no cheek-pouches, but, on the other hand, the stomach is complicated by sacculations or pouches, and the last lower molar has a posterior heel, thus carrying five cusps. The thumb is small or absent, the callosities on the buttocks are also small, and the nails are narrow and pointed. The laryngeal sac (or throat-sac) opens in the middle line of the front of the larynx, and is formed by an extension of the thyro-hyoid membrane. The true langurs, of the genus Semnopithecus, in which a small thumb is retained, form a large group confined to south-eastern Asia, where it ranges from India and the Himalaya to Borneo and Sumatra by way of Burma, Cochin China and the Malay Peninsula. A well-known representative is the sacred hanuman monkey (S. entellus) of India, which, like the larger Himalayan S. schistaceus, is slate-coloured; the Bornean S. hosei, on the other hand, is wholly maroon-red. Other species, like the Indian S. johni, have the head crested. The allied genus Rhinopithecus, as typified by the orange snub-nosed monkey, R. roxellanae (fig. 9), of eastern Tibet and Szechuen, is characterized by the curiously short and upturned nose and the long silky hair of the back, especially in the winter coat. In the typical species the predominating colour is orange, tending to yellowish-olive on the back; but in R. bieti of the mountains bordering the valley of the Mekon and R. brelichi of Central China it is slaty-grey. The third Asiatic genus is represented by the proboscis monkey (Nasalis larvatus) of Borneo, in which the nose is extraordinarily elongated. The nose of the adult male is commonly represented as projecting straight out from the face, but it really bends down to overhang the upper lip; it is much shorter in the female, and quite small and bent upwards in the young. (See Langur and Proboscis Monkey.)
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| (From Milne-Edwards.) |
Fig. 9.—The Orange Snub-nosed Monkey (Rhinopithecus roxellanae).
The African guerezas, forming the genus Colobus, differ from their Asiatic cousins by the total loss of the thumb. Some of these monkeys, like Colobus satanas of West Africa, are wholly black; but in others, such as C. guereza (or abyssinicus), C. sharpei and C. caudatus of North-east and East Africa, forming the sub-genus Guereza, there is much long white hair, which in the species last named forms a mantle on the sides of the body and an elongated fringe to the tail, thus assimilating the appearance of the animal to tie long lichens hanging from the boughs of the trees in which it dwells. Most or all of the Semnopithecinae feed on leaves; a circumstance doubtless correlated with the complex structure of their stomach.
Cercopitheques, Mangabeys, Macaques and Baboons.-The whole of the remaining members of the family Cercopithecidae are included in the sub-family Cercopithecinae, which presents the following characteristics: The hind limbs are not longer than the front pair; the tail may be either long, short or practically absent; cheek-pouches are present; the stomach is simple; the callosities on the buttocks are often very large; the last lower molar may or may not have a posterior heel; and the thumb is well developed. Whereas all the Senmopithecinae are completely arboreal, many of the Cercopithecinae, and more especially the baboons, are to a great extent, or entirel terrestrial. The typical representatives of the group are the African monkeys, forming the genus Cercopithecus, which includes very large number of species with the following characters in common: the tail, although shorter than in the Semnopithecinae, is long, as are the hind limbs, while the general form is slender. The jaw and muzzle are short and the cheek-pouches large; while the nose is not prominent, with the nostrils approximated; whiskers and a beard of variable length are usually developed. The fingers of the long hands are united by webs at the base; the thumb is small in comparison with the great toe. The callosities are of moderate size; and the hairs of the thick and soft fur are in most cases marked by differently-coloured rings. For convenience of description the numerous species of this genus may be arranged in a number of groups or sub-genera. The first of these groups includes the spot-nosed forms (Rhinostictus), characterized by the presence of a spot of white, red or blue on the nose; well-known species, being the lesser white-nosed guenon (C. petaurista) of West Africa and the hocheur, C. nictitans, which is also West African. In the typical group, as represented by the malbrouck monke (C. cynosurus) of the West Coast, and the Abyssinian grivet (C. sabaeus), the fur of the back is of a more or less olive-green hue, while the under surface and whiskers are white and the limbs grey. The large patas monkey (C. patas) of West Africa and the red-backed monkey (C. pyrrhonotus) of Kordofan typify a third section (Erythrocebus), characterized by the red upper and white lower surface of the body. A fourth section (Mona) includes the mona (C. mona) of Western, and Sykes's monkey (C. albigularis) of Eastern Africa, with a number of allied species, characterized by the presence of a black band running from the outer angle of the eye to the ear, and the black or dark-grey limbs. The bearded monkey (C. pogonias) of Fernando Po and Guinea, with two sub-species, typifies a small section (Otopithecus), characterized by large rufous or yellowish ear-tufts and the presence of three black stripes on the forehead. Pagonocebus is another small section, including the well-known Diana monkey (C. diana) of Western, and De Brazza's monkey (C. neglectus) of Eastern Africa, easily recognized by the long (generally white) beard and frontal crest. Finally, the little talapoin (C. talapoin) of the Gaboon alone represents a group (Miopithecus) broadly distinguished by having three, in place of four, cusps on the crowns of the lower molars.
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| (From Milne-Edwards.) |
Fig. 10.—The Tibet Macaque (Macacus arctoides tibetanus).
The next group is that of the African mangabeys (Cercocebus), the more typical species of which are easily recognized by their bare flesh-coloured eyelids, and the absence of rings of different colours on the hair, or at least on that of the back. In these monkeys the general form is intermediate between that of the cercopitheques and the macaques, to be next mentioned, the head being more oval and the muzzle more produced than in the former, but less so than in the latter. The limbs are longer and the body is more slender than in the macaques, and the callosities are also smaller. On the other hand, the thumb is smaller than in the guenons, and the tail is carried curled over the back instead of straight; while these monkeys differ from the former in having a posterior heel to the last lower molar, which is thus five-cusped, as in the macaques. The laryngeal air sacs of the latter are, however, wanting. Well-known representatives of the typical section of the group are the sooty mangabey (C. fuliginosus) and the white-collared mangabey (C. collaris) of West Africa, the latter easily recognized by the bright red crown of the head. A second group of the genus, Lophocebus (or Semnocebus) is typified by the white-cheeked mangabey (C. albigena) of the equatorial forest-region, in which the head is crested and the eyelids lack bare flesh-coloured rims. The rhesus monkey (Macacus rhesus) of India is the typical representative of the macaques, which may be regarded as the Asiatic representatives of the mangabeys. From that group the macaques differ by their heavier and stouter build (fig. 10), thicker limbs, the presence of large laryngeal sacs, the larger size of the callosities, and the more produced muzzle, while many of them have the tail (which may be absent) much shorter. The nostrils are not terminal, and the hairs are generally ringed. In habits the macaques are much more terrestrial than the mangabeys, some of them being completely so. In the typical group, which, in addition to the rhesus, includes the Himalayan macaque (M. assamensis), the brown macaque (M. arctoides) of Burma and Tibet (fig. 10), the tail may be about equal to half the length of the body or less; but in the Barbary ape, M. (Inuus) inuus, of North Africa and Gibraltar, this appendage is wanting. In a third group (Nemestrinus), represented by the pig-tailed macaque (M. nemestrinus), ranging from Burma to Borneo, and the lion-macaque (M. leoninus) of Siam, the tail, which is carried erect, is about one-third the length of the body. The lion-tailed macaque (M. silenus) of southern India, often miscalled the wanderoo, represents a group by itself (Vetulus) characterized by the long hair fringing the face and meeting under the chin, and the tufted lion-like tail, which is from one-half to three-quarters the length of the body. The last group (Cynomolgus), now often regarded as a distinct genus, is typified by the widely-spread crab-eating macaque (M. cynomolgus), characterized by its produced muzzle, short and stout limbs, and basally-swollen tail, which is nearly as long as the body. It also includes the South Indian bonnet-macaque (M. sinicus) and the Ceylon toque-macaque (M. pileatus), taking their names from the elongated hair on the crown, which are nearly allied, and with the first-named species approach the baboons in their elongated muzzles (see Macaque).
Fig. 11.—The Yellow Baboon (Papio cynocephalus).
A still nearer approach to the baboons is made by the black ape (Cynopithecus niger) of Celebes and the neighbouring islands, which is represented by several sub-species, among them the so-called Moor-macaque (Macacus maurus). Some difference of opinion exists as to the proper serial position of this species, which is included in Macacus by several zoologists who separate Cynomolgus as a genus. It is characterized by the marked elongation of the muzzle, which, like the neck, hands and feet, is naked. The nostrils are, however, directed outwards and downwards, as in the macaques; but, on the other hand, there are baboon-like ridges on the sides of the muzzle and heavy supra-orbital ridges. There are large cheek-pouches; and the tail is a mere stump. The colour is sooty-black. The weird-looking gelada baboon (Theropithecus gelada) of southern, and the allied T. obscurus of eastern Abyssinia represent a genus which is essentially baboon-like in general characteristics, but has the nostrils of the macaque-type, while the facial portion of the skull is shorter than the cranial. The preorbital portion of the face is concave with the ridges rounded, and the tusks are very long. The long tail is tufted at the tip, and the hair is long and bushy, developing into a mantle-like mane on the forequarters of old males, leaving the chest bare. The general colour is dark-brown. The last representatives of the Circopithecidae are the baboons, or dog-faced baboons, of Africa and Arabia, forming the genus Papio. These are for the most part large monkeys, associating in herds under the leadership of an old male, and dwelling chiefly among rocks, although they ascend trees in search of gum. They are easily recognized by their long dog-like faces (fig. 11), in which the nostrils open at the extremity of the greatly elongated muzzle. On the sides of the muzzle are prominent longitudinal ridges covered with bare skin which may be brilliantly coloured. The callosities, which are also generally bright-coloured, are large; and the tail is of moderate length or short. The hairs are ringed with different colours, and the general colour is olive-yellow, grey or brownish. The typical, and at the same time the smallest representative, of the group, is the yellow baboon (P. cynocephalus or P. babuin) (fig. 11), ranging from Abyssinia to Angola and Mozambique, and distinguished by its rather short and grooved muzzle and longish tail, which is nearly as long as the body. The majority of the species, such as the widely spread P. anubis (with several local races), P. sphinx of West Africa, and the chacma (P. porcarius) of South Africa, are included in the sub-genus Chaeropithecus, and have the muzzle longer and undivided and the tail shorter, in most the colour is golden-olive with very distinct rings, but in the chacma it is darker. The hamadryad baboon, P. hamadryas, of north-east Africa and Arabia, and the closely allied P. arabicus of southern Arabia, represent a sub-genus (Hamadryas) characterized by the ashy-grey colour and the profuse mantle-like mane of the adult males; the tail being slightly shorter than the body. Lastly, the West African mandrill (P. maimon) and drill (P. leucophaeus) form the sub-genus Maimon, distinguished by the extremely short tail, and the great development of the facial ridges, which are strongly fluted. In the mandrill, which is the most brilliantly coloured of all mammals, the ridges are vermilion and cobalt, while the callosities on the buttocks are of equal brilliance; but in the drill, which has white ear-tufts, the colouring is more sombre (see Baboon and Mandrill).
American Monkeys and Marmosets.—The monkeys and marmosets of tropical America constitute the Platyrrhina, or second section of the Anthropoidea, and are characterized as follows: An additional premolar is present in both jaws, bringing up the number of these teeth to three pairs. The tympanum is ring-like, with no external bony-tube, or meatus; and a tympanic bulla exists. A parieto-zygomatic suture causes the jugal bone to be included in the orbital plate; and the orbito-temporal foramen is large. Cheek-pouches and callosities on the buttocks are wanting. The descending colon does not form a sigmoid flexure; and the caecum is generally bent in a hook-like form, with, at most, very slight narrowing of its terminal extremity. The cartilage forming the inter-nasal septum is broad, and the nostrils are directed obliquely outwards. The tail, which never has fewer than fourteen vertebrae, is generally as long as the body, and frequently prehensile. The ethmoturbinals are originally separate; and the laryngeal sac, when present, is of peculiar type. Usually there is only a simple primary discoid placenta, but rudiments of a secondary one have been recently described.
The first family, or Cebidae, includes the American monkeys, as distinct from marmosets, which present the following characteristics: The ears are more or less naked externally. The terminal joints of the fingers and toes carry flat or curved nails; and the thumb, when present, is opposable to the other fingers. Except in the uakaris, the tail is long, generally short-haired, and frequently with a terminal bare surface for pretension. Dentition i. 22, c. 11, p. 33, m. 33. Generally a foramen (entepicondylar) in the inner side of the lower end of the humerus. As a rule, only a single offspring is produced at a birth. Ranging over tropical America, the Cebidae have their headquarters in the vast Brazilian forests, where so many of the animals are more or less arboreal in their habits. These monkeys are completely arboreal, more so, indeed, than the gibbons among the Catarrhina.
The first sub-family, Alouatinae, is represented only by the howlers, Alouata (or Mycetes), characterized) by the long prehensile tail with the extremity naked below, the well-developed thumb, and the extension of the hyoid-bone into an enormous bladder-like chamber contained between the two branches of the lower jaw (fig. 3). In this bony cup is received one of the three or five laryngeal sacs. There are about half a dozen species, with several sub-species; three of the best known being A. seniculus, A. belzebul and A. ursina. Several are brilliantly coloured, with bright or golden hair on the flanks; but in the Amazonian A. nigra the male is black and the female straw-coloured. The muzzle is longer than in other Cebidae (see Howler).
Fig. 12.—The White-cheeked Capuchin (Cebus lunatus).
The Cebinae include the typical members of the family, characterized by the large brain, of which the elongated hemispheres cover the cerebellum; the brain-case of the skull being, of course, elongated in proportion. The lumbar vertebrae are short, with upright comb-like processes, instead of the rhomboidal ones of the howlers. The lower jaw and hyoid are of normal form. In the first section of the sub-family the tail is evenly haired throughout, the thumb well developed, the limbs of medium length, with the front not longer than the hind pair, the nails curved, and the humerus with an entepicondylar foramen. The typical genus Cebus includes the numerous species of capuchins, many of which are so commonly seen in captivity. They are stouter in build and smaller in size than the spider-monkeys, and their tails are only prehensile to a small extent, but are commonly carried spirally rolled. The conical upper canines project below the upper lip, and the molars have blunt low cusps. Well-known species are the white-cheeked capuchin, C. lunatus (fig. 12), of south Brazil; the true capuchin, C. capucinus, ranging from Guiana to Brazil; and the brown capuchin, C. fatuellus, of Guiana; all of these showing the black crown from which these monkeys take their popular name. The most northern representative of the group is the white-throated C. hypoleucus, which ranges to Costa Rica. The squirrel-monkeys, Chrysothrix (or Saimiris), of which C. sciureus is the most familiar representative, are not infrequently placed in the Nyctipithecinae, although their true position seems to be here. They differ from Cebus by their smaller size and more delicate build, by the tail being scarcely at all prehensile, by the smaller canines, smaller and more sharply cusped molars, and the large and closely-approximated orbits, whose inner walls are partly membranous (see Capuchin and Squirrel-Monkey).
Fig. 13.—Geoffroy's Spider-Monkey (Ateles geoffroyi).
The second section of the sub-family includes the spider-monkeys (fig. 13), and is characterized by the completely prehensile tail, with the inner surface of the tip naked, the rudimentary condition or absence of the thumb, the laterally compressed and more or less pointed nails, and the absence of an entepicondylar foramen to the humerus. The limbs, too, are very long and slender, with the front pair of greater length than the hind ones. The caecum approximates to that of the Catarrhina, having its terminal extremity pointed. The true spider-monkeys (Ateles) lack the thumb, and have the nails but slightly compressed and pointed, the limbs very long, the nasal septum of ordinary width, and the fur not woolly. Nearly all have the hair on the head, except that of the forehead, directed forwards. There are nearly a dozen species. In these monkeys so powerful is the grasp of the tail that the whole body can be sustained by this organ alone. It even serves as a fifth hand, as detached objects, otherwise out of reach, can be grasped by it, and brought towards the hand or mouth. Their prehension is in other respects exceptionally defective, owing to the loss of the thumb. Spider-monkeys are very gentle in disposition; and, by this and their long limbs and fitness for tree-life, seem to represent the gibbons of the Old World. Nevertheless, in spite of their admirable adaptation for arboreal life, their comparatively slow progression offers a marked contrast to the vigorous agility of the gibbons (see Spider-Monkey). The brown spider-monkey (Brachyteles arachnoides) of south Brazil alone represents a genus connecting the preceding in some degree with the next, a rudimentary thumb being present, while the fur is woolly, the nails are much compressed, and the nostrils more approximated than usual. In the woolly spider-monkeys of the genus Lagothrix (fig. 14) not only is the fur woolly, but the thumb is fairly well developed; the nails are like those of Brachyteles, but the nostrils are normal. Humboldt's spider-monkey, L. humboldti (or L. lagotrica) and the dusky spider-monkey, L. infumata, both of which occur in Brazil and Amazonia, alone represent this genus.
Fig. 14.—Humboldt's Woolly Spider-Monkey (Lagothrix humboldti).
Some half-dozen species of the monkeys known as sakis (Pithecia) form the typical representatives of the sub-family Pithecinae, in which the tail, even when long, is non-prehensile, while the lower incisors are slender and inclined forwards in a peculiar manner, with a gap on each side separating them from the long canine. The hemispheres of the brain cover the cerebellum, the brain-case is elongated, and, despite the absence of a laryngeal sac, the lower jaw is deep with a large angle, thus recalling that of the howlers. There is no caecum. In all cases the thumb is well developed. The arrangement of the hair is very variable. From the other members of the group the sakis are sufficiently distinguished by the long and bushy tail; while they are further characterized by having a large head. In some cases the hair on the crown of the head is divided by a transverse parting, so as to overhang the upper part of the face. P. satanas of Pará and P. chiropotes of Guiana are well-known species. The uakaris (Uacaria or Cothurus) of Amazonia are broadly distinguished from all other Cebidae by their short or rudimentary tails; Ua. calva being remarkable for its brilliant red jaw and pale chestnut hair (see Uakari).
Fig. 15.—Lemur-like Douroucouli (Nyctipithecus felinus).
The last and lowest representatives of the Cebidae constitute the sub-family Nyctipithecinae, the members of which are cat-like monkeys, with woolly or bushy hair, short, conical muzzles, non-prehensile tails and well-developed thumbs. The brain-case of the skull is not elongated, and the hemispheres of the brain do not cover the cerebellum. The lumbar vertebrae are elongated, with long, sharp, backwardly directed spinal processes; the hinder part of the lower jaw is tall; and there is no laryngeal sac. The long and hooked caecum has its terminal portion constricted. In accordance with their nocturnal habits, the douroucoulis (Nyctipithecus) are easily recognized by their large and closely approximated eyes, which are, however, separated by a complete septum, the comparatively narrow nasal septum, small ears buried in the woolly fur, and long bushy tail. Well-known species are the lemur-like douroucouli (N. felinus, fig. 15) of Amazonia, Peru and Ecuador, and N. vociferans, with a nearly similar distribution. The titis, Callithrix (or Callicebus[2]), are smaller monkeys (fig. 16), with more forwardly directed eyes, which are not surrounded by a radiating fringe of hair and a wider nasal septum. The titis are represented by about ten species, of which C. moloch is represented in fig. 16. Most of them are confined to Amazonia, but a few among them C. moloch, reach the east coast. Like the marmosets, they feed largely upon insects and grubs.
Fig. 16.-The Moloch Titi (Callithrix moloch).
Fig. 17.-The Golden Marmoset (Hapale chrysoleuca).
The second and last family of the Platyrrhina is represented by the marmosets or oustitis (Hapalidae), all of which are small monkeys, with the ears hairy externally, and the nails, except that of the great toe, claw-like, the thumb non-opposable, the tail long, bushy and non-prehensile, and only two molars in each jaw, the dental formula thus being i. 22, c. 11, p. 33, m. 22. The humerus has no entepicondylar foramen. Three young are produced at a birth. Marmosets are divided into two genera, those in which the lower canines are not markedly larger than the incisors constituting the typical Hapale, while such as have the lower canines taller than the teeth between them form the genus Midas. These squirrel-like little monkeys, in which the great toe can be opposed to the other toes, range as far north as 15° N., where they are represented by Midas geoffroyi, and as far in the opposite direction as the southern tropic, where M. chrysopygus and M. rosalia occur. The colour and the length of the hair are very variable, some species having long silky pale-chestnut hair (fig. 17) and tufted ears, while in others the hair is comparatively short and black, or black with brown bars, while the ears are not tufted (see Marmoset).
Fig. 18.-Skull of Ring-tailed Lemur (Lemur catta).
| uc, | Upper canine. | | pm, | Premolars. |
| lc, | Lower canine. | m, | True molars. |
Lemurs, Prosimiae.—Although the likeness generally takes the form of a more or less grotesque caricature, the faces of all monkeys and apes present, in greater or less degree, some resemblance to the human countenance. In the lower group of Primates, commonly known as lemurs, or lemuroids, this resemblance is wholly lost, and the face assumes an elongated and fox-like form, totally devoid of that “expression” which is so characteristic of man and the higher apes and monkeys. Lemurs, Prosimiae or Lemuroidea, which form a group confined to the tropical regions of the Old World and more numerously represented in Madagascar than elsewhere, are arboreal and for the most part crepuscular or nocturnal Primates, feeding on insects or fruits, or both together and collectively characterized as follows. The tail, which is generally long and thickly haired, is never prehensile. As a rule, there is a single pair of pectoral teats, but an additional abdominal or even inguinal pair may be present. The thumb and great toe are opposable to the other digits, the former being provided with a flat nail, while the second toe is always furnished with a claw; the fourth toe is longer than all the rest, and the second, or index, finger is small or rudimentary. In the skull (fig. 18) the orbital ring is formed by the frontal and jugal bones, and, except in the Tarsiidae, there is a free communication between the orbit and the temporal fossa; the lachrymal foramen is situated outside the orbit (fig. 18), the tympanic either forms a free semicircle in the auditory bulla or enters into the formation of the latter; and the foramen rotundum is generally fused into the spheroidal fissure. Interparietal bones are frequently developed, and the two halves of the lower jaw are generally welded together in front. Except in the genus Perodicticus, the humerus is furnished with an entepicondylar foramen at the lower end; the centrale of the carpus is generally free; and the femur is usually provided with a third trochanter. The cerebellum is only partially covered by the hemispheres of the brain, which in the medium-sized and larger species conform to the general type of the same parts in monkeys and apes. The normal dental formula is i. 22, c. 11, p. 33, m. 33, or the same as in American monkeys; but the upper incisors are small and separated from each other, while the lower ones are large and approximated to the incisor-like canine; the molars have three or four cusps. In all cases the stomach is simple and a caecum present. The testicles are contained in a scrotum, the penis has a bone, the uterus is bicornuate and the urethra perforates the clitoris. The placenta may be either diffuse, with a large allantoic portion, and non-deciduate, or discoidal and deciduate. As a rule, only a single offspring is produced at a birth. Very noteworthy is the occurrence in the females of the Asiatic lorisis of what appears to be the vestige of a marsupial apparatus, attached to the front of the pelvis. Lemur catta also possesses the rudiment of a marsupial fold; while in both sexes of the aye-aye occurs a skin-muscle corresponding to the sphincter marsupii of marsupials.
The distribution of existing lemurs is very peculiar, the majority of the species inhabiting Madagascar, where they for the most part dwell in small patches of forest, and form about one-half the entire mammalian fauna of the island. The remaining species inhabit Africa south of the Sahara and the Indo-Malay countries.
Tarsier.—The tiny little large-eyed Malay lemuroid known as the tarsier, Tarsius spectrum (or T. tarsius), of the Malay Peninsula and islands, together with its Celebean and Philippine representatives, alone constitutes the section Tarsiina (and the family Tarsiidae), which has the following distinctive characteristics: The lower incisor is vertical and the canine of normal form, while the upper incisors are in contact; the orbit is cut off from the temporal fossa by a bony plate, leaving only a small orbital fissure; the tympanum enters into the formation of the auditory meatus, through which passes the canal for the internal carotid artery; the tibia and fibula in the hind-leg are fused together, and the calcaneum and navicular of the tarsus elongated. The tarsier seems to be a primitive form which makes a certain approximation to the Anthropoidea, and ditiers from other lemuroids in the structure of its placenta. The dental formula is i. 21, c. 11, p. 33, m. 33, total 34. Tarsiers have enormous eyes, occupying the whole front of the orbital region, and are purely nocturnal in their habits, living in trees on the branches of which they move by hopping, a power they possess owing to the elongation of the tarsal bones (see Tarsier).
Malagasy Lemurs.—All the other Prosimiae may be grouped in a second section, the Lemurina, characterized as follows: The lower incisors and the canine are similar in form and inclined forwards (fig. 18); the upper incisors are small and separated by an interval in the middle line; the orbits communicate largely with the temporal fossae; the internal carotid artery enters the skull in advance of the auditory meatus through the foramen lacerum anterius; and the tibia and fibula are separate. The Malagasy lemurs are now all included in the single family Lemuridae, which is confined to Madagascar and the Comoro Islands, and characterized by the tympanic ring lying free in the auditory bulla. The typical sub-family Lemurinae, which includes the majority of the family group, is characterized by all the fingers except the index having flat nails, the elongation of the facial portion of the skull, the large hemispheres of the brain not covering the cerebellum, the occasional presence of two inguinal in addition to the normal pectoral teats, the dental formula i. 22, c. 11, p. 33, m. 33, with the first upper incisor generally small and sometimes wanting, and the hinder cusps of the upper molars smaller than the front ones. These lemurs are woolly-haired animals, often nearly as large as cats, with the legs longer than the arms, the tail long and bushy, and the spinal processes of the last dorsal and the lumbar vertebrae inclined. In the typical genus Lemur (fig. 19), the tarsus is of normal length, the tail at least half as long as the body, the ears are tufted, there are no inguinal teats, the last premolar is not markedly broader than the others, and the upper molars have a conspicuous cingulum. These lemurs have long fox-like faces, and habitually walk on the ground or on the branches of trees on all fours, although they can also jump with marvellous agility. They are gregarious, living in small troops, are diurnal in their habits, but most active towards evening, when they make the woods resound with their loud cries, and feed, not only on fruits and buds, but also on eggs, young birds and insects. When at rest or sleeping, they generally coil their long, bushy tails around their bodies, apparently for the sake of the warmth it affords. They have usually a single young one at a birth, which is at first nearly naked, and is carried about, hanging close to and almost concealed by the hair of the mother's belly. After a while the young lemur changes its position and mounts upon the mother's back, where it is carried about until able to climb and leap by itself. One of the most beautiful species is the ring-tailed lemur (L. catta, fig. 19), of a delicate grey colour, and with a long tail marked with alternating rings of biack and white. This is said by G. A. Shaw to be an exception to other lemurs in not being arboreal, but living chiefly among rocks and bushes. Pollen, however, says that it inhabits the forests of the south-west parts of Madagascar, living, like its congeners, in considerable troops, and not differing from them in its habits. He adds that it is extremely gentle, and active and graceful in its movements, and utters at intervals a little plaintive cry like that of a cat. All the others have the tail of uniform colour. The largest is L. varius, the ruffed lemur, sometimes black and white, and sometimes reddish-brown, the variation apparently not depending on sex or age, but on the individual. In L. macaco the male is black and the female red L. mongoz, L. fulvus and L. rubriventer are other well-known species.
Fig. 19.—The Ring-tailed Lemur (Lemur catta).
In all these lemurs the small upper incisors are not in contact with one another or with the canine, in front of which they are both placed. In the species of Hapalemur, on the other hand, the upper incisors are very small, sub-equal and separated widely in the middle line; those of each side in contact with each other and with the canine, the posterior one being placed on the inside, and not in front of the latter. Muzzle very short and truncated. Two inguinal teats, in addition to the normal pectoral pair, are present. The last premolar is broader than those in front, and the upper molars lack a distinct cingulum. The typical H. griseus is smaller than any of the true lemurs, of a dark-grey colour, with round face and short ears. It is quite nocturnal, and lives chiefly among bamboos, subsisting on the young shoots. The second species has been named H. simus. In Hapalemur there is no free centrale to the carpus, and the same is the case with the six or seven species of Lepidolemur (Lepilemur), in which the first upper incisor is rudimentary or wanting, while the second may also be wanting in the adult. There are small lemurs, with small premaxillae, short snouts, tails shorter than the body, bladder-like mastoid processes, and the upper molars with an inconspicuous cingulum and the hind-cusps of the last two rudimentary; the fourth upper premolar being relatively broad. Mixocebus caniceps is an allied generic type (see Lemur).
The small Malagasy lemurs of the genera Chirogale, Microcebus and Opolemur differ from the preceding in the elongation of the calcaneum and navicular of the tarsus, on which grounds they have been affiliated to the African galagos. The difference in the structure of the tympanum in the two groups indicates, however, that the elongation of the tarsus has been independently developed in each group. These lemurs have short, rounded skulls, large eyes, long hind limbs and tail, large ears, the first upper incisor larger than the second, the last upper premolar much smaller than the first molar and furnished with only one outer cusp, and the mastoid not bladder-like. Some are less than a rat in size, and all are nocturnal. One of the largest, Microcebus fufcifer, is reddish-grey, and distinguished by a dark median stripe on its back which divides on the top of the head into two branches, one of which passes forwards above each eye. The most interesting peculiarity of these lemurs is that certain species (Opolemur samati, Chirogale milii, &c.) during the dry season coil themselves up in holes of trees, and pass into a state of torpidity, like that of the hibernating animals in the winter of northern climates. Before this takes place an immense deposit of fat accumulates upon certain parts of the body, especially the basal portion of the tail. The smallest species, M. pusillus, lives among the slender branches on the tops of the highest trees, feeding on fruit and insects, and making nests like those of birds.
In the sub-family Indrisinae the dentition of the adult consists of thirty teeth, usually expressed by the formula i. 21, c. 11, p. 22, m. 33; but possibly i. 32, c. 10, p. 32, m. 33. In the milk-dentition there are twenty-two teeth, the two additional teeth in the fore part of the lower jaw having no successors in the permanent series. Hind limbs greatly developed, but the tarsus normal, the great toe of large size, and very opposable; the other toes united at their base by a fold of skin, which extends as far as the end of the first phalange. The thumb is but slightly opposable; and all the fingers and toes are hairy. The length of the tail is variable. Two pectoral teats. Caecum very large, and colon extremely long and spirally coiled. The brain is large and the thorax wide.
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| (From Milne-Edwards and Grandidier.) |
Fig. 20.—The Indri (Indris brevicaudatus).
The animals of this group are essentially arboreal, and feed exclusively on fruit, leaves, buds and flowers. When they descend to the ground, which is but seldom, they sit upright on their hind legs, and move from one clump of trees to another by a series of short jumps, holding their arms above them in the air. Among them are the largest members of the order. The genus Indris has the upper incisors sub-equal in size; upper canine larger than the first premolar, muzzle moderately long, ears exserted. Carpus without an os centrale. Tail rudimentary. Vertebrae: C.7, D.12, L.9, S.4, Ca.9. The indri (I. brevricaudatus, fig. 20), discovered by Sonnerat in 1780, is the largest of the group, and has long woolly hair, partly brown and partly white. In the sifakas, Propithecus, of which there appear to be three species, with numerous local races, the second upper incisor is much smaller than the first. Upper canine larger than the first premolar. Muzzle rather short. Ears short, concealed by the fur. An os centrale in the carpus. Tail long. Vertebrae: C.7, D.12, L.8, S.3, Ca.28. In Avahis, represented only by A. laniger, the second upper incisor is larger than the first. Upper canine scarcely larger than the first premolar. Muzzle very short. Ears very small and hidden in the fur, which is very short and woolly. Carpus without os centrale. Tail long. Vertebrae: C.7, D.11, L.9, S.3, Ca.23 (see Indri and Sifaka).
The last sub-family, Chiromyinae (formerly regarded as a family), is represented only by the aye-aye, Chiromys (or Daubentonia) madagascariensis, and has the following characteristics: Dentition of adult, i. 11, c. 00, p. 10, m. 32, total 18. Incisors (fig. 21) very large, compressed, curved, with persistent pulps and enamel only in front, as in rodents. Teeth of cheek-series with flat indistinctly tuberculated crowns. In the young, the first set of teeth more resemble those of normal lemurs, being i. 22, c. 10, m. 22, all very small. Four teats, inguinal in position, a feature peculiar to this species. All the digits of both feet with pointed, rather compressed claws, except the great toe, which has a flattened nail; middle digit of the hand excessively attenuated. Vertebrae: C.7, D.12, L.6, S.3, Ca.27 (see Aye-Aye).
Fig. 21.—Skull of the Aye-aye (Chiromys madagascariensis).
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| (From A. Milne-Edwards.) |
Fig. 22.—The Slow Loris (Nycticebus tardigradus).
Galagos and Lorises.—The lemurs of Africa and the Indo-Malay countries-commonly miscalled sloths—differ from the Lemuridae in that the tympanic enters into the formation of the auditory meatus, in consequence of which they are referred to a family by themselves, the Nycticebidae, which is in turn divided into two sub-families, Galaginae and Nycticebinae. The African galagos or Galaginae, which have the same dental formula as the Lemuridae, are distinguished by the elongation of the calcaneum and navicular of the tarsus. In the single genus Galago, with the sub-genera Otolemur and Hemigalago, the last upper premolar, which is nearly as large as the first molar, has two large external cusps. Vertebrae: C.7, D.13, L.6, 5.3, Ca.22-26. Tail long, and generally bushy. Ears large, rounded, naked and capable of being folded at the will of the animal. Teats four, two pectoral and two inguinal (see Galago). The lorises, Nycticebinae (Lorisinae), are distinguished as follows: Index-finger very short, sometimes rudimentary and nailless. Fore and hind limbs nearly equal in length. Tarsus not specially elongated. Thumb and great toe diverging widely from the other digits, the latter especially being habitually directed backwards. Tail short or rudimentary. Teats two or four. Lorises and pottos (as the African representatives of the group are called) are essentially nocturnal, and remarkable for the slowness of their movements. They are completely arboreal, their limbs being formed only for climbing and clinging to branches, not for jumping or running. They have rounded heads, very large eyes, short ears and thick, short, soft fur. They feed, not only on vegetable substances, but, like many of the Lemuridae, also on insects, eggs and birds, which they steal upon while roosting at night. One of the greatest anatomical peculiarities of these animals is the breaking up of the large arterial trunks of the limbs into numerous small parallel branches, constituting a rete mirabile, which is found also in the sloths, with which the lorises are sometimes confounded on account of the slowness of their movements. The Asiatic lorises, which are divided into two genera, are characterized by the retention of the normal number of phalanges in the small index-finger, and the presence of a pair of minute abdominal teats (the existence of which has only recently been discovered by Messrs Annandale and Willey). In the slow lorises, forming the genus Nycticebus (fig. 22), the first upper incisor is larger than the second, which is often early deciduous. Inner margin of the orbits separated from each other by a narrow flat space. Nasal and premaxillary bones projecting but very slightly in front of the maxillae. Body and limbs stout. No tail. Vertebrae: C.7, D.17, L.6, S.3, Ca.12. The single species N. tardigradus, with several races, inhabits eastern Bengal, the Malay countries, Sumatra, Borneo, Java, Siam and Cochin China. These lorises lead solitary lives in the recesses of large forests, chiefly in mountainous districts, where they sleep during the day in holes or fissures of large trees, rolled up into a ball, with the head between the hind legs. On the approach of evening they awake, and during the night ramble among the branches of trees slowly, in search, of food, which consists of leaves and fruit, small birds, insects and mice. When in quest of living prey they move noiselessly till quite close, and then suddenly seize it with one of their hands. The female produces but one young at a time. In the second genus, represented only by the slender loris (Loris gracilis) of southern India and Ceylon, the upper incisors are very small and equal. Orbits very large, and only separated in the middle line above by a thin vertical plate of bone. Nasals and premaxillae produced forwards considerably beyond the anterior limits of the maxillae, and supporting a pointed nose. Body and limbs slender. No external tail. Vertebrae: C.7, D.14, L.9, S.3, Ca.6. The slender loris is about the size of a squirrel, of a yellowish-brown colour, with large, prominent eyes, pointed nose, long thin body, long, angularly bent, slender limbs and no tail. Its habits are like those of the rest of the group. The Indian and Ceylon races are distinct (see Loris).
The African pottos, Perodicticus, differ by the reduction of the index-finger to a mere nailless tubercle, and apparently by the absence of abdominal teats. In the typical section of the genus there is a short tail, about a third of the length of the trunk. Two or three of the anterior dorsal vertebrae have very long slender spinous processes which in the living animal project beyond the general level of the skin forming distinct conical prominences, covered only by an exceedingly thin and naked integument. P. potto, the potto, is one of the oldest known members of the lemuroids having been described in 1705 by Bosman, who met with it in his voyage to Guinea. It was, however, lost sight of until 1835, when it was rediscovered in Sierra Leone. It is also found in the Gaboon and the Congo, and is strictly nocturnal and slower in its movements even than Nycticebus tardigradus, which otherwise it much resembles in its habits. A second species, P. batesi, inhabits the Congo district. A third species, the awantibo (P. calabarensis), rather smaller and more delicately made, with smaller hands and feet and rudimentary tail, constitutes the sub-genus Arctocebus. It is found at Old Calabar, and is very rare. Vertebrae: C.7, D.15, L.7, S.3, Ca.9.
Extinct Primates
The most interesting of all the extinct representatives of the order is Pithecanthropus erectus (q.v.), which is represented by the imperfect roof of a skull, two molars and a femur, discovered in a bed of volcanic ash in Java. The forehead is extremely low, with beetling brow-ridges, and the whole calvarium presents a curiously gibbon-like aspect. The capacity of the brain-case is estimated to have equalled two-thirds that of an average modern man. The creature is regarded as transitional between the higher apes, more especially the Hylobatidae and the lowest representatives of the genus Homo, such as the Neanderthal men. From the Lower Pliocene of India has been obtained the palate of a chimpanzee-like ape, which by some is referred to the existing Anthropopithecus, while by others it is considered to represent a genus by itself—Palaeopithecus. The same formation has yielded the canine tooth of a large ape, apparently referable to the existing Asiatic genus Simia. From the Miocene of Europe has been described the genus Dryopithecus, typified by D. fontani, a generalized ape of the size of a chimpanzee, related, perhaps, both to the Simiidae and the Hylobatidae. The Lower Pliocene of Germany has yielded other remains referred to a distinct genus under the name of Paidopithex rhenanus. From the Miocene of the Vienna basin Dr O. Abel has described certain ape-remains under the name of Griphopithecus suessi, as well as others regarded as representing a species of Dryopithecus with the name D. darwini. As regards the first, all that can be said is that it indicates a member of the group to which Dryopithecus belongs. It has been suggested that the latter genus is closely related to man, but this idea is discountenanced by the great relative length of the muzzle and the small space for the tongue. Teeth of another man-like ape from the Tertiary of Swabia, described under the preoccupied name Anthropodus, have been re-named Neopithecus. The genus Anthropodus is represented by remains of an ape of doubtful position from the French Pliocene. Pliopithecus from the French Miocene is certainly a gibbon, perhaps not distinguishable from Hylobates.
Oreopithecus, from the Miocene of Tuscany, is perhaps intermediate between gibbons and baboons (Papio), the latter of which, as well as Macacus, are represented in the Indian Pliocene. Mesopithecus, of the Grecian Lower Pliocene, presents some characters connecting it with Semnopithecus and others with Macacus. An allied type from the Lower Pliocene of France is Dolichopithecus, taking its name from the elongated skull; while Macacus occurs in the Upper Pliocene and Pleistocene of several parts of Europe. Cryptopithecus, from the Swiss Oligocene, appears to be the oldest known Old World monkey. From the Miocene of Patagonia are known certain monkeys described as Homunculus, Anthropops, &c., apparently more akin to the Cebidae but perhaps representing an extinct family.
Fig. 23.—Skull and Hinder Right Upper Cheek-teeth of Megaladapis madagascariensis.
Passing on to the lemurs, it may be mentioned in the first place that G. Grandidier has described an extinct lemur from the Tertiary of France, which he believes to be nearly related to the slow lorises, and has accordingly named Pronycticebus gaudryi. If the determination be correct the discovery is of interest as tending to link the modern faunas of southern India and West Africa (which possess many features in common) with the Tertiary fauna of Europe. Certain remarkable extinct lemuroids of large size have been discovered in the superficial deposits of Madagascar, in one of which (Megaladapis) the upper cheek-teeth are of a tritubercular type (fig. 23), while in the second and smaller form (Nesopithecus) the dentition makes a notable approximation to that of the Cercopithecidae. Each of these genera, which probably survived till a very late date, is generally regarded as typifying a family group. In Megaladapis the skull is distinguished by its elongation and the small size of the eye-sockets, the tritubercular upper molars presenting considerable resemblance to those of the living Lepidolemur. The brain is of a remarkably low type. In one species the approximate length of the skull is 250, and in the second 330 millimetres. Even more interesting are the two large species of Nesopithecus, one of which was at first described as Globilemur. They show a very complicated type of brain, and were at first regarded as indicating Malagasy representatives of the Anthropoidea. In regard to the character of the tympanic region of the skull this genus shows several features characteristic of the more typical Malagasy lemuroids; and the eye-sockets are open behind, while the dentition is numerically the same as in some of the latter. On the other hand, in several features Nesopithecus resembles the Anthropoidea; the upper incisors are not separated in the middle line, and the upper molars present the pattern found in the Cercopithecidae, while in one species the lachrymal bone and foramen are within the orbit. The resemblances to apes are not confined to the skull, but are found in almost all the bones. Probably the genus may be regarded as a specialized lemuroid. The Oligocene and Eocene formations of Europe and North America have yielded remains of a number of primitive lemuroids, grouped together under the name of Mesodonta or Pseudolemures, and divided into families severally typified by the genera Hyopsodus, Notharctus, Anaptomorphus and Microchoerus (Necrolemur), of which the last two are European and the others American. To particularize the characteristics of the different families would occupy too much space, and only the following features of the group can be mentioned. The dental formula is i. 33, c. 11, p. 44 or 22, m. 33. The canines are often large; the upper molars carry from three to six cusps, while the lower ones are of the tuberculo-sectoral type with either four or five cusps. The lachrymal foramen may be either within or without the orbit, which is in free communication with the temporal fossa, with or without a complete bony ring. The humerus has an entepicondylar foramen. It is specially noteworthy that Adapis resembles the Lemuridae in the form and relations of the tympanic ring. Anaptomorphus has large orbits and tritubercular molars. Certain Middle and Lower Eocene North American genera, such as Mixodectes and Pelycodus, together with the European Plesiadapis and Protoadapis, which have been regarded as lemuroids, are now frequently referred to the Rodentia (q.v.). On the other hand, Metachiromys, of the Bridger Eocene of America, originally described as a relative of Chiromys, has been stated to be an armadillo.
Literature.—The above article is based on the articles Ape and Lemur in the 9th edition of this encyclopedia. The following are the chief works on the subject: H. O. Forbes, “A Handbook to the Primates,” Allen's Naturalists' Library (2 vols., 1904); A. A. W. Hubrecht, “The Descent of the Primates” (New York, 1897); “Furchung und Keimblatt-bildung bei Tarsius spectrum,” Verh. Ac. Amsterdam (1902); C. J. Forsyth Major, “Our Knowledge of Extinct Primates from Madagascar,” Geol. Magazine, decade 7, vol. vii. (1900); “Skulls of Foetal Malagasy Lemurs,” Proc. Zool. Soc. (London, 1899); “The Skull in Lemurs and Monkeys,” ibid. (1904); H. Winge, “Jordfundne og nulevende Aber” (Primates), E. Mus. Lundi (1895); C. Earle, “On the Affinities of Tarsius,” American Naturalist (1397); W. Leche, “Untersuchungen über das Zahnsystem lebender und fossiler Halbaffen,” Gegenbaurs Festschrift (Leipzig, 1896); E. Dubois, “Pithecanthropus erectus, eine menschenähnliche Uebergangsform aus Java” (Batavia, 1894); A. Keith, “On the Chimpanzees and their relationship to the Gorilla,” Proc. Zool. Soc. London (1899); W. Rothschild, “Notes on Anthropoid Apes,” ibid. (1905); O. Schlaginhaufen, “Das Hautleistensystem der Primatenplanta,” Morphologisches Jahrbuch, vols. iii. and xxxiv. (1905); G. E. Smith, “The Morphology of the Occipital Region of the Cerebral Hemisphere in Man and Apes,” Anatomischer Anzeiger, vol. xxiv. (1904); H. F. Standing, “Primates from Madagascar,” Trans. Zool. Soc., 1908, 18, pp. 59-216. (R. L.*)