1911 Encyclopædia Britannica/Swine
SWINE, a name properly applicable to the domesticated pig (Sus scrofa), but also including its wild relatives. As stated in the article Artiodactyla, these animals typify the family Suidae, which, with the Hippopotamidae, constitute the section Suina, a group of equal rank with the Pecora. The Suidae are divisible into the true Old World swine (Suinae) and the American peccaries (Dicotylinae). Of the former the leading characteristics are as follows: an elongated mobile snout, with an expanded, truncated, nearly naked, flat, oval terminal surface in which the nostrils are placed. Feet narrow, with four com- pletely developed toes on each. Hoofs of the two middle toes with their contiguous surfaces flattened. The outer toes not reaching to the ground in the ordinary walking position. Teeth variable in number, owing to the suppression in some forms of an upper incisor and one or more premolars.
In the typical genus Sus, as exemplified by domesticated pigs (see Pig) and the wild boar (see Boar), the dentition is ».|, c.\, p.\, m.\; total 44; the upper incisors diminishing rapidly in size from the first to the third, and the lower incisors long, narrow, closely approxi- mated, and almost horizontal in position, their tips inclining towards the middle line, the second slightly larger than the first, the third much smaller. The tusks or canines are strongly developed, with
Fig. 1. — Dentition of Boar (Sus scrofa).
persistent roots and a partial enamel covering, those of the upper jaw not having the usual downward direction, but curving out- wards, upwards and finally inwards, while those of the lower jaw are directed upwards and outwards with a gentle backward curve, their hinder edges working and wearing against the front edges of the upper pair. The tusks appear externally to the mouth, the form of the upper lip being modified to allow of their protrusion, but are much less developed in females than in males. The teeth of the molar series gradually increase in size and complexity from first to last, and are arranged in contiguous series, except that the first lower premolar is separated by an interval from the second. First and second upper premolars with compressed crowns and two roots; and the third and fourth with an inner lobe of the crown, and an additional pair of roots._ The first and second molars have quadrate crowns, with four principal obtuse conical cusps, around which numerous accessory cusps are clustered. The crown of the third molar is nearly as long as those of the first and second together, having, in addition to the four principal lobes, a large posterior heel, composed of clustered conical cusps, and sup- ported by additional roots. The lower molars resemble generally those of the upper jaw, but are narrower. Milk dentition : i.\, c.\, m.\ ; total 28 — the first permanent premolar having no predecessor. The third incisor in both upper and lower jaws is large, developed before the others, with much the size, form and direction of the canine. Vertebrae: C. 7, D. 13-14, L. 6, S. 4, Ca. 20-^24. The hairy covering of the body varies under different conditions of climate, but when best developed, as in the European wild boar, consists of long stiff bristles, abundant on the back and sides, and of a close softer curling under-coat.
All the typical swine are further characterized by the fact that the young are longitudinally striped with bands of dark brown and some paler tint ; this striped coat disappearing in the course of a few months. On the other hand, this peculiar marking is rarely seen in domestic pigs in any part of the world, although it has been occasionally observed. It is stated by Darwin that the pigs which have run wild in Jamaica and New Granada have resumed this aboriginal character, and produce longitudinally striped young; these being the descendants of domestic animals introduced from Europe since the Spanish conquest, as before that time there were no true pigs in the New World. Another character by which the European domesticated pig differs from any of the wild species is the concave outline of the frontal region of the skull.
In the wild boar (Sus scrofa) the upper or hinder surface of the lower tusk, which has no enamel, inclines obliquely outwards and is broader than the outer surface. The distributional area
Fig. 2. — Wild Boar and Young (Sus scrofa).
of this species includes northern Africa, Europe and central and northern Asia as far as Amurland. Whether the Nubian 5. senarensis is really distinct, seems doubtful. To the same group belongs the Indian 5. cristatus, distinguished by the more pronounced development of the crest of long hairs on the nape of the neck, and closely related to the next species. The third species is the banded pig 5. vittatus, of Sumatra, characterized by having a broad reddish or whitish band running from the middle of the snout along the upper lip to disappear on the side of the neck; the skull being short and high, with the facial portion of the lachrymal bone small. Races of this type are also met with in Java, Cochin-China and Formosa; the pig from the latter island having been named 5. taivanus. Near akin is the Japanese 5. leucomystax and the small Andamanesc 5. andamanensis. Whether the New Guinea 5. papuensis and 5. niger arc really indigenous members of this group or modified descendants of European tame pigs is doubtful; although the general character of the Papuan fauna supports the idea that they are introduced. A second group is typified by the warty pig, S. verrucosus, of Java, in which the hinder or upper unenamelled surface of the lower tusk is narrower than the outer, concave, and set nearly in the long axis of the skull. The skull itself is elongated, with comparatively simple and primitive molars, the latter being relatively short. There are also three small warts on each side of the face, the largest of which is just below the eye and carries long bristles. The small S. celebensis of Celebes and S. philippinensis are probably only varieties of this species. The bearded pig S. barbatus (= longirostris) of Borneo is a very distinct member of this group, distinguished by the great elongation of the skull, and the presence of a tuft of long hair near the muzzle. In Sumatra it is represented by the subspecies 5. b. öi, and in south-west Borneo by S. b. gargantua.
Some doubt exists whether the pygmy hog of the Nepal Terai, which is not much larger than a hare, is best regarded as a member of the typical genus, under the name of Sus salvanius or as representing a genus by itself, with the title Porcula salvania.
Similar doubts have also been entertained with regard to the African bush-pigs or river-hogs, but from geographical considerations alone these are but regarded as representing a separate genus, Potomochoerus, although they are nearly allied to the verrucosus group of Sus. They are specially distinguished by the great development of the anterior half of the zygomatic arch of the skull, and by the presence in the boars of a horny protuberance of the skin in front of each eye, which overlies a tuberosity on the nasal bone; the molars are also small and simple, and the anterior premolars are generally shed at an early stage of life. The group is represented in Madagascar, as well as in Africa south of the Sahara. (See River-Hog.)
The recently discovered Hylochoerus of the equatorial forest-districts of Africa comes nearest to the under-mentioned wart-hogs, but the skull is of a much less specialized type, while the upper tusks are much smaller although they have the same general curvature and direction, and the cheek-teeth lack the peculiar characteristics of those of Phocochoerus, although they present a certain approximation thereto. On the other hand, resemblance to that genus is shown by the reduction of the upper incisors to a single pair. The skin is clothed with a thick coat of coarse black hair of a bristly nature, but there are a few whitish hairs on the face and in the groin.
In the African wart-hogs (Phacochoerus), which take their name from the large warty lobes projecting from each side of the face, the teeth are remarkably modified. The milk-dentition, and even the early condition of the permanent dentition, is formed on the same general type as that of Sus, except that certain teeth arc absent, the formula being i ⅓, c ¼, p ⅔, m ⅔, total 34.; but as age advances all the teeth have a tendency to disappear, except the canines and the posterior molars, but these, which in some cases are the only teeth left in the jaws, attain an extraordinary development. The upper canines especially are of great size, and curve outwards, forwards and upwards. Their enamel covering is confined to the apex, and soon wears away. The lower canines are much more slender, but follow the same curve; except on the posterior surface, their crowns are covered with enamel ; both pairs of canines are large in the two sexes. The third or last molar tooth of both jaws is of great size, and presents a structure at first sight unlike that of any other mammal, being composed of numerous (22-25) parallel cylinders or columns, each with pulp-cavity, dentine and enamel-covering, and packed together with cement. Examination will, however, show that a modification similar to that which has transformed the com- paratively simple molar tooth of the mastodon into the extremely complex grinder of the Indian elephant has served to change the tooth of the common pig into that of Phacochoerus. The tubercles which cluster over the surface of the crown of the common pig are elongated and drawn out into the columns of the wart-hog, as the low transverse ridges of the mastodon's tooth become the leaf-like plates of the elephant's molar. (See Wart-Hog.)
The last existing representative of the Suidae is the babirusa of Celebes, alone representing the genus of the same name, and readily distinguished by the extraordinary size and form of the tusks of the old males. (For the characteristics of this animal see Babirusa.)
Extinct Swine.—Species of Sus are met with in PKocenc strata of Europe and Asia, the Lower Pliocene 5. arymanthius of Greece and S. gitanleus and 5. titan of India being enormous animals; the last with comparatively simple molars. The European S. palaeochoerus and the Indian S. hysudricus are smaller forms; the first exhibiting signs of relationship with Polamochoerus. In India also occurs Hippohyus distinguished by the extremely complicated structure of its molars. In the European Miocene we have Hyotherium and Palaeochoerus, and in the Upper Oligocenc Propalaeochoerus, which have square molars without any tendency to a selenodont structure in their cusps. Curiously enough a selenodont type is, however, apparent in those of the imperfectly known Egyptian Geniokyus of the Upper Eocene, the earliest species which can be included in the family. Even in this the forward direction of the lower incisors is noticeable. Choeropotamus is a European Oligocene genus with bunodont molars which show a conspicuous basal cingulum in the lower dentition; the first premolar is absent. In the European Miocene Listriodon, which also occurs in the Indian Tertiarics, the molars have a pair of transverse ridges, like those of the proboscidean Dinotherium (q.v.); but the genus is believed to be related to the Oligocene Doliockoerus and Choerolherium, in which these teeth show a more normal type of structure.