HIPPOPOTAMUSES, PIGS, AND DEER 285 



developments, one species of True Swine developing to the size 

 of a rhinoceros. 



The True Pigs have usually six incisors in both jaws, though 

 in two African genera the upper incisors tend to disappear, a 

 tendency parallel to what has occurred among the Ruminants. 

 As already mentioned, the pigs have " bunodont " molars with 

 short crowns, that is to say, the surface of the molar tooth is 

 divided into a number of blunt hillocks. The most striking 

 feature of the True Pigs lies in the canine teeth. In the upper 

 jaw, instead of growing vertically downwards, as in almost all 

 other mammals, they curve outwards and upwards, and this 

 tendency is carried to such an extreme in the Oriental genus 

 Babirusa that the upper canine teeth turn right round from their 

 sockets, and grow straight upwards through bone and flesh. 

 An archaic feature in the pigs is the number of mammae (from 

 five to three pairs), and their distribution along the ventral 

 region. To this may be added, perhaps, their tendency towards 

 an omnivorous diet, a characteristic shared by the allied peccaries 

 of America. Although this feature is carried to a much greater 

 extreme in the domestic than in the wild pig, still nearly all 

 forms of pig will eat, in addition to various vegetable sub- 

 stances — roots, fruits, nuts, and herbage — animal matter, as 

 represented by snakes, lizards, young birds and beasts, and 

 carrion. Pigs, also, are unlike other existing Ungulates (except 

 one or two species of deer), in that they produce ordinarily more 

 than two young at a birth. Their digestive organs are relatively 

 simple and primitive. 



An early type of pig (Sus palaochcerus)^ and a gigantic swine 

 as large as a tapir {Sus erymanthius\ reached England during the 

 Pliocene Epoch, and Sus erymanthius may have lingered on into 

 the Pleistocene and the time of man's coming to this country. 

 But with this doubtful exception man has only known one wild 

 pig in these islands, the wild boar, unless, as some zoologists 

 have thought, another wild species of pig of a more slender type, 

 more like the wild pigs of Eastern Asia, existed in Ireland, and gave 

 rise to the domestic greyhound pig, which is now nearly extinct. 



