250 



VERTEBRATA. 



manent tusks, composed entirely of dentine, are preceded by two 

 deciduous smaller ones. The structure of the molars is exceed- 

 ingly complex, but there is only one molar at a time in 

 each jaw. The proboscis is a long flexible organ, known aa 

 the trunk ; it is terminated by a thumb-like appendage, and 

 encloses a double tube, between which and the integument is 

 a thick layer of muscular substance. The cranial cavity is very 

 small, the immense size of the head being due to the enormous 

 development of the frontal sinuses. This peculiarity depends on 

 the necessity of supporting the tusks, and of affording sufficient 

 surface for the attachment of muscles to work the trunk. There 

 are no clavicles. The stomach is simple, the intestines very long 

 and voluminous, and the caecum of large size. The placenta is 

 zonary and deciduate. 



The elephant is herbivorous ; every thing it eats is put into its 

 mouth by its trunk. There are two species Elephas indicus, 

 with smaller ears and the males alone with well-developed tusks ; 

 and E. africanus (separated as a genus Loxodon by Gray), with 

 large ears and well-developed tusks in both sexes ; the enamel is 

 also markedly different. A third species, the mammoth (E. primi- 

 genius), is now extinct, but it was once common in England. 

 Fossil species are somewhat numerous ; their remains have been 

 found in all parts of the world ; one of them, Dinotherium, has 

 been regarded as a dugong and as a Marsupial. Like Mastodon 

 and the extinct elephants, it belonged to the Miocene period. 



ElepJiantid(e. Dinotheriid<B. 



*Mastodon. *Dinotherium. 



Elephas (Elephant). 



Order IX. UNGULATA. 



Toes never more than four, protected by hoof-like nails, and 

 incapable of grasping. No clavicles. Placenta non-deciduate. 



There are two sets of enamelled teeth ; canines are not often 

 present ; the lower incisors are sometimes wanting, and the upper 

 incisors in most of the ruminants are replaced by a callosity of 

 the gum. There are generally six molars on each side of either 

 jaw ; these teeth are deeply penetrated by the enamel, and are of a 

 massive character. In the pig family and musk-deer the canines 

 are in the form of tusks. 



Many of the Ungulata are furnished with horns. These are of 

 various kinds : a solid prolongation of bone, covered by the skin 

 and persistent, as in the giraffe ; a solid outgrowth of the frontal 



