202 PHILOSOPHY OF ZOOLOGY, 



113. Mastodon. Summits of the grinders with tuber- 

 cular processes, the points of which become flat by the 

 wearing down of the enamel and ivory. This is an extinct 

 genus, the remains of the species of which are found in the 

 debris of large rivers. 



Without a snout. 



114. Rhinoceros. Three hoofs on each foot. Nose 

 horned. There appears to be some reason for considering 

 the three recent species as the types of as many genera. 

 CuviEii assigns twenty-eight grinders to all of them, but 

 from the observations of Mr Bell, the R. sumatrensis has 

 only twenty-four *. This species has two incisors in each 

 jaw. In the R. Indktis, there are two incisors above^ and 

 four below, while in the R. Africanus^ there are none. The 

 skin of the R. Indicus is folded, that of the others is near- 

 ly smooth. 



APODA. 



Hind-feet united with the tail in the form of a fin. 



The skin on the body is smooth, and nearly destitute of 

 appendices. The fingers are all enveloped in skin, with- 

 out a protruded arm, and form a fin or swimming paw. 

 They are destitute of separate hind-feet and tail, but their 

 place is supplied by a broad horizontal expansion, posteri- 

 orly emarginate, which, though differing in direction, serves 

 the same purpose as the caudal fin in fishes, and is the 

 principal organ of progressive motion. The horizontal 

 position of this fin is probably connected with the vertical 

 motion of the animal, in coming to the surface, at intervals, 



• Phil. Trans. 1793, p. 3. Tab. ii, iii,, where there is a good figure of the 

 animal and the cranium. 



