1392 



CLASS MAMMALIA. 



ent pulps, are present either in the upper or lower jaws of the 

 males of all the forms at present known. The cheek-teeth may attain 

 extreme complexity ; and the true molars always consist of transverse 

 ridges, which may vary greatly in height, and may be either uninter- 

 rupted, or split up into inner and outer columns, which may have a 



more or less alternate arrangement ; 

 there are never fewer than three 

 such ridges in the last milk and the 

 first true molars ; and the intervening 

 valleys may be either entirely open, 

 or blocked by accessory tubercles, or 

 completely filled with cement. The 

 toes are all invested in a common 

 integument, although furnished with 

 distinct broad hoofs ; and the third 

 digit of each foot is the largest. 

 There are two anterior venae cavae 

 entering the right auricle of the 

 heart ; the stomach is simple ; there 

 is a large caecum ; the testes are 

 permanently retained in the abdo- 

 men ; the uterus has two cornua ; 

 and the placenta is non-deciduate 

 and zonary. 



In the skull and dentition the 

 members of this suborder are de- 

 cidedly specialised ; but in other 

 respects, such as the structure of 

 the limbs, and the presence of two 

 venae cavae, they show very gene- 

 ralised features ; and there are not 

 wanting indications of a remote 

 affinity with the Rodents, and per- 

 haps the Sirenia. It will be shown 

 as we proceed that the structure of the cheek-dentition has ad- 

 vanced from a comparatively generalised type in Dinotherium to 

 an extremely specialised one in the existing species of Elephants; 

 and it appears that this specialisation " has followed to a consider- 

 able extent a line analogous to that obtaining in the Perissodactyla 

 and Artiodactyla, and shows itself in the increased height and com- 

 plexity of the crowns of these teeth and in the final attainment of a 

 nearly horizontal and continuous plane of wear. From the structure 

 of the cheek-teeth in the more generalised members of the suborder, 

 it may be inferred that the action of the molars of one jaw upon 

 those of the other must have been mainly a scissor-like or snapping 



Fig. 1265. — Dorsal aspect of the left pes 

 of the Indian Elephant (Elephas indicus). 

 Greatly reduced. (After Cuvier.) The 

 numbers indicate the digits. The upper- 

 most bone is the calcaneum, resting upon 

 which is the astragalus, with its flat tibial 

 surface. The bone with a long narrow 

 dorsal surface immediately below the astra- 

 galus is the navicular ; while the one sup- 

 porting the metatarsals of the fourth and 

 fifth digits is the cuboid. 



