THE PERISSODACTYLA. 



293 



In the skull, the tympanic bone is small ; and, as in sun- 

 dry other Mammals, the root of the pterygoid jDrocess of the 

 sphenoid is perforated by an aperture or canal. 



The posterior premolar teeth are, generally, very like the 

 molars. The stomach is simple, and the caecum exceedingly 

 large. 



The teats are inguinal, or situated in the groin. When 

 the head is provided with horny appendages, they are entire* 

 ly epidermal and devoid of a bony core ; and they are placed 

 in the middle line of the skull. 



» i'' 





*: \ 



Fio. 93. — A, Front aspect of the left tarsus of a Horse. — ^1. Calcaneiim. 2. Asti-agalua. & 



Naviculare. 4. Ectocuneiform. 5. Caboides. 

 B, Posterior aspect of the left metatarsus of a Horse. — ^1. The metatarsal of the third digit, 



2, 3. The metatarsals of the rudimentary digits. 



The JPerissodactyla consist of the existing families Equidm^ 

 Mhinocerotidm^ and Tapiridoe, and of the extinct Palceothe- 

 ridoB and Macrauchenidoe. 



