90 OSTEOLOGICAL GALLERY. 



premolar and molar teeth in one unbroken series, the posterior 

 premolars much resembling the true molars in shape and size. 

 The dorsal and lumbar vertebrae together number at least twenty- 

 two ; and, as in all other Ungulates, clavicles are entirely absent. 



The three existing families of this Suborder, the Rhinocerotida, 

 Tapirida, and Equidce, are sharply separated by the structure of 

 their molar teeth and by the numbers of their toes ; these families 

 are, however, very closely connected by numerous intermediate 

 fossil forms, the majority of which have been found in North 

 America. Such are the Lophiodontida, the oldest Perissodactyles, 

 from the Lower and Middle Eocene, allied to the Tapirs ; and the 

 Hyracodontidce, Macrauchennda, Chalicotheriid<je,aud. Palaeotheriidce, 

 all more or less allied to Rhinoceros, but showing, the further we 

 go back in time, a closer relationship one to another. These various 

 fossil forms are described in the Guide to the Geological Galleries, 

 pp. 21-23. 



["Case 10.] The Rhinoceroses, of which a remarkably fine series of skeletons 

 is placed in the centre of the Gallery, with skulls in Case 10, are 

 characterized by the. thickness and solidity of their bones, by the 

 structure of their molar teeth, and by the enlargement of their 

 nasal bones to serve as supports for the external horns. Incisor 

 teeth are entirely wanting in the adults of the African species ; 

 but in the Indian there is a pair of large ones above, and 

 two large and two small ones below. Of the specimens exhibited 

 the most noteworthy are the skeleton of the Indian Rhinoceros 

 (R. unicornis), and the two fine skulls of the White Rhinoceros 

 (R. simus), by far the largest of the group, placed in the front of 

 Case 10. 



[Case 11.] The Tapirs (Case 11, Divs. A-D) present almost the same 

 osteological characters as their ancestors, which are found fossil 

 in deposits of Upper Miocene age; they belong therefore to one of 

 the oldest existing types of Mammals. Their molar teeth have two 

 simple transverse crests on their crowns, very different from the 

 highly complex enamel foldings of the teeth of Rhinoceroses and 

 Horses. Their nasal bones are small ; their toes four in number 

 on the fore, and three on the hind feet. 



c ^ e The Horses (Equida) (Case 11, Divs. E and F, and Case 12) 



11 & 12.1 f t ne present day consist of animals in which the gradual loss of 



the outer digits in the feet has proceeded further than in any other 



