Group I.— Suina

Fam. 1. Hippopotamidae.—The family Hippopotamidae contains of existing genera only Hippopotamus, for the Liberian dwarf Hippopotamus is not now regarded, as it was formerly, as the type of another genus, Choeropsis. The reasons for its former separation were the loss of the outer pair of incisors and the different proportions of various parts of the skull. This little Liberian animal has, however, been shown by Sir W. Flower to possess the missing incisors occasionally; and as to the proportions of the skull, it is exceedingly common for small animals to vary from larger relatives in this way. Hence, considering the characteristic features of the Hippopotamus and the fewness of species, it seems unnecessary to divide it up further. We shall therefore only recognise one genus.

The Hippopotamus at present is African in range, and confined to that continent. But quite recently it inhabited Madagascar; and further back still in time the existing African species, H. amphibius, ranged into Europe; there were also Indian forms, which were contemporary with the Stone-age man. The Common Hippopotamus is a great thick-skinned beast with but few hairs. It has four toes on each foot, a complex stomach, but no caecum. The strong incisors continue growing through life, as do the great canines. The number of incisors is two on each side of each jaw. Some of the extinct species had six in each jaw, and they were distinguished as a genus Hexaprotodon, contrasting with Tetraprotodon, until intermediate conditions were observed. Choeropsis, as already observed, was a still further reduction of the tetraprotodont type. The molars (the formula is Pm 4/4 M 3/3) when worn show a double trefoil pattern. The orbital cavity is encircled by bone. As with many other aquatic mammals the kidneys are lobulated.

Fig. 140.—Hippopotamus. Hippopotamus amphibius. × 1⁄40.

A very singular fact about the Hippopotamus is the production of a "bloody sweat," a carmine-coloured secretion, containing small crystals and corpuscles, from the skin. This coloured fluid has of course nothing to do with blood.

The animal grows to a length of at any rate 14 feet. The limbs and the tail are short. Like other aquatic animals the nostrils are on the surface of the head, and can be closed when the animal is under water. When it reaches the surface of the water after a prolonged immersion, it spouts like a Whale. Sir Samuel Baker says that ten minutes is the longest time that the Hippopotamus can remain below the water. It is frequently a dangerous animal to encounter, as it will capsize boats, and even bite large pieces out of their bottoms; with its huge teeth it can and does attack and destroy human beings. The Hippopotamus not only swims, but can walk along the bottom of a river with great rapidity. It occasionally puts out to sea from the mouths of rivers frequented by it; and it is supposed that in this way Madagascar was populated with Hippopotamuses, whose remains are now found in swamps in that island.

Fig. 141.—Wild Boar. Sus scrofa. × 1⁄12.

Fam. 2. Suidae.—The Pig family, Suidae, differ from the last in their smaller size, in the terminal nostrils and mobile snout, which is not grooved, except faintly as in Babirusa. They are generally hairy, but the Babyroussa is an exception, while Phacochoerus is but slightly haired. Though there are four digits, as in the Hippopotamus, only two reach the ground in walking. The stomach, furthermore, is simple, and (except in Dicotyles) there is a caecum. The kidneys are smooth, and the liver is more lobate than in Hippopotamus. The orbital cavity is confluent with the temporal fossa. The typical genus, Sus, is distributed over Europe, Asia, and the islands of the Malay Archipelago, reaching as far as Borneo and Celebes. The dentition is complete. A single species, the so-called S. sennaariensis, is from Ethiopian Africa, but it is not certain how far this animal may be an escaped species introduced by man. A very large number of "species" of Sus have been described, but Dr. Forsyth Major is disposed to reduce them to four if not to fewer species. He allows the widely-ranging S. scrofa, S. vittatus, and the eastern Malayan S. verrucosus and S. barbatus.

Fig. 142.—Pygmy Hog (from Nature). Sus salvania. × 1⁄6.

The Pygmy Hog of the Bhotans seems to be not entitled to specific rank, certainly not to generic (in the opinion of some), though it has been termed Porcula salvania. The Wild Boar of Europe is Sus scrofa. It was formerly quite abundant in this country; not merely are its remains exhumed from fens, caves and peat bogs, but there is ample evidence of its continuance down to a comparatively late historic period. Enactments are on record as to the hunting of these animals; there are places, such as Boarstall, whose names are clearly derived from the name of the animal, presumably once a native of the locality; and various documents all show the presence of the Wild Boar in this country down to so late a period as the end of the sixteenth century.

Fig. 143.—Wart Hog. Phacochoerus aethiopicus. × 1⁄6.

The African Wart Hog, genus Phacochoerus, is usually regarded as the type of a distinct genus of Pigs. This animal, "superlatively ugly" with its huge tusks and great protuberances upon the face, is chiefly to be distinguished from the genus Sus by these characters, and by the complexity of the last molar, which, with the tusks, are sometimes in aged animals the only teeth left. The complete formula is Pm 2/2 M 3/3. There are two species of this genus, P. aethiopicus and P. africanus. When enraged the Wart Hog is said to carry its tail directly up, and to present a ludicrous as well as ferocious appearance.

Fig. 144.—Head of Wart Hog.

The Celebesian Babyroussa, genus Babirusa, is an almost hairless hog with enormously upturned tusks in both jaws of the male. In the Wild Boar there is a hint of this, which is carried still further in Phacochoerus; but in Babirusa the upper tusks turn upwards before they leave the substance of the jaw, for which reason they appear to arise on its dorsal surface; the lower tusks are nearly as long. It has been found that the young of this Pig are not striped as are those of other Pigs. By means of the curved upper tusks this animal has been said by old writers to suspend itself to branches of trees, just as does by his downwardly-projecting tusks the male Chevrotain! There is but one species, B. alfurus.

From Sus proper the African and Malagasy Potamochoerus, including the Red River Hog, is barely separable generically. Their principal claim to generic distinction lies in the existence of a horny outgrowth arising from a bony apophysis above the canine in the male. These have been compared to the osseous "horn cores" in the extinct Dinocerata. But the Javan Sus verrucosus shows at least the beginning of a similar modification. The popular name of the animal is derived from the fine rufous colour of its pelage, not seen, however, in all the species. Dr. Forsyth Major recognises five species, of which only one is from Madagascar.

Fig. 145.—Peccary. Dicotyles tajaçu. × 1⁄6.

Fam. 3. Dicotylidae.—The Peccaries are generally placed in a different family from that of the other Pigs. This family, Dicotylidae, contains but one genus, Dicotyles, with at most two species. The name of the animal is connected with the dorsal gland; the animal thus appeared to possess two navels. The Peccaries, exclusively confined to the New World, differ from the Old-World Pigs in one or more important characters. They have only three toes on the hind-feet, and the stomach is complicated. Though the Peccaries have but small tusks they hunt in packs and are very dangerous animals to meet with. They owe, too, their safety from many foes to their sociable habits. Being nocturnal animals they are liable to the attacks of the Jaguar, which will speedily overpower and devour a Peccary that has strayed from its herd.

Fossil Swine.—The existing genera of the Pig tribe are also known in a fossil condition. Sus itself goes back as far as the Upper Miocene. Sus erymanthius, the Erymanthine Boar, is known from beds of that age in Greece, England, and Germany. This genus is not known to have had a wider distribution in the past than it has in the present. Dicotyles occurs in the Pleistocene of both North and South America, the regions which it inhabits at the present day. The genus Listriodon, also Miocene, is remarkable for having lophodont instead of bunodont teeth, that is so far as concerns the molars, which resemble those of the Tapir. It was European and Indian in range. A number of genera, more remote from the existing Pigs than those which have just been dealt with, are placed together in a special sub-family, Achaenodontinae. The type genus, Achaenodon, had a somewhat short skull for a Pig; and it is in general aspect and in the characters of the canine teeth highly suggestive of that of a Carnivore. The bunodont molars, however, are Suine, as is the form of the lower jaw with a rounded angle. This is an Eocene animal found in Wyoming.

Elotherium occurs chiefly in the Miocene of both North America and Europe; but E. uintense is Eocene. The orbits are completely encircled by bone in the more modern forms; this is not the case in the last-described genus, with which E. uintense agrees. The skull is also longer and more Pig-like. The zygomatic arch is powerful, with sometimes a large descending process, such as is found in Diprotodon, more faintly in Kangaroos, and in Sloths and certain extinct Edentates. The lower jaw has a pair of dependent processes near the symphysis, which suggest processes occupying a corresponding position in Dinoceras. The skull and body are heavy, but the two-toed limbs are slender. There is a smaller pair of toes behind these. The dentition is complete, and the canines are not inordinately developed. The brain is very diminutive. Perhaps E. uintense should be separated as a distinct genus, Protelotherium.

Hyotherium (which is regarded as identical with Palaeochoerus) has a sharp sagittal crest; the orbit is nearly but not quite closed. The canines are not strongly developed. The upper canines have double fangs as in Triconodon among extinct mammals, and as in the Hedgehog and other forms among living Mammalia. The premolars have the cutting and serrated edge of those of some other Pigs, a feature which gives them a curious resemblance to the "grinding" teeth of Seals. The molars are tuberculate, and like those of living Pigs. It is European and Indian in range, and Miocene.

The genus Choeropotamus has a complete dental formula save for the loss of a premolar in the lower jaw. Though it has lost this tooth, it is from an older stratum than some of those forms which have retained that premolar; it has been found in the Upper Eocene of the Isle of Wight and of the neighbourhood of Paris.

The American and Miocene Chaenohyus has lost the corresponding teeth of the upper jaw.

Homacodon is a genus consisting of several species, which has a bunodont and complete dentition. The molars are sextubercular in the upper jaw. H. vagans was of about the size of a Rabbit, and it appears to have had a curved neck. The limbs had five digits, as is so generally the case with Eocene Ungulates. It is known from the Middle Eocene of Wyoming.