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.
