CATALOGUE 



OF 



UNGULATE S. 



VOL. Y. 



SUBORDER IL— PERISSODACTYLA. 



At the present day the "odd-toed" imguktes are much less 

 uumerously represented than the Artiodactyla, comprising, 

 as they do, only three family groups, with a relatively small 

 number of genera and species. In the middle and early 

 part of the Tertiary epoch they were much more abundant. 

 They are distinguished from the Artiodactyla by the 

 following characters. 



The toes, of whicli there may be four, three, or one on 

 the fore-feet, but only three or one on the hind-feet, severally 

 correspond, when three are present (fig. 1, B), to the second, 

 third, and fourth of the typical pentadactyle series, and to 

 the third when the number is reduced to one ; the additional 

 digit sometimes retained in the fore-limb representing the 

 fifth of the full series ; in all cases the toe corresponding to 

 the third of the typical series is symmetrical in itself, and 

 larger than the second and fourth, when these are retained. 

 The number of the combined dorsal and lumbar vertebra? 

 never falls below twenty-two, and, in existing forms, is 

 usually twenty-three. An alisphenoid canal traverses the- 

 bones of the base of the hind part of the skull, on the uj)per 

 aspect of which there is a more or less marked expansion of 

 the superior extiemities of the nasal bones. Very generally 

 the premolar teeth, with the exception of the first, are of the 

 V. B 



