288 UNGULATA 



entirely devoid of hair. With regard to the curiously modified 

 dentition, Wallace (Malay Archipelago, vol. i. p. 435) makes the 

 following observations: "It is difficult to understand what can 

 be the use of these horn- like teeth. Some of the old writers 

 supposed that they served as hooks by which the creature could 

 rest its head on a branch. But the way in which they usually 

 diverge just over and in front of the eye has suggested the more 

 probable idea, that they serve to guard these organs from thorns 

 and spines while hunting for fallen fruits among the tangled thickets 

 of rattans and other spiny plants. Even this, however, is not 

 satisfactory, for the female, who must seek her food in the same 

 way, does not possess them. I should be inclined to believe 

 rather that these tusks were once useful, and were then worn 

 down as fast as they grew, but that changed conditions of life have 

 rendered them unnecessary, and they now develop into a monstrous 

 form, just as the incisors of the Beaver and Rabbit will go on 

 growing if the opposite teeth do not wear them away. In old 

 animals they reach an enormous size, and are generally broken off 

 as if by fighting." 



Phacochcerus. 1 The Wart-Hogs, so called from the large 

 cutaneous lobes projecting from each side of the face, have 

 the teeth still more remarkably modified than in Babirusa. 

 The milk -dentition, and even the early condition of the per- 

 manent dentition, is formed on the same general type as that 

 of Sus, except that certain of the typical teeth are absent, the 

 formula being i J, c ^, p -f , m ^, total 34 ; but as age advances all 

 the teeth have a tendency to disappear, except the canines and the 

 posterior molars, which in some cases are the only teeth left in 

 the jaws, and 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. Unlike those of the Babirusa, the canines 

 of the Wart^Hog are large in both sexes. The third 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. Careful 

 examination will, however, show that a similar modification to that 

 which has transformed the comparatively 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 ; and, as already mentioned, some of the fossil 

 Indian and African species of Sus indicate the mode in which this 

 1 Cuvier, Regne- Animal, vol. i. p. 236 (1817). 





