XIX.] 



UNGULA TA. 



319 



tyle foot of the Rhinoceros and the monodactyle foot of 

 the Horse are met with in extinct species of the Perisso- 

 dactyla. 



rl.^ 



Fig. 118. — Dorsal surface of right tarsus 

 of Rhinoceros {Rhi>ioceros su>?iatre7t- 

 sis, \. 



Fig. 119 — Dorsal surface of right tarsus 

 of Horse [Eqiius cahallus), \. 



In the Ai'tiodactyla the third and fourth digits are nearly 

 equally developed, and their ungual phalanges are flattened 

 on their contiguous sides, so that together they constitute a 

 symmetrical form. The second and fifth toes, when present, 

 are also equal, but smaller than the others. A line drawn 

 though the centre of the foot has on its tibial side the 

 third digit and metatarsal, the external cuneiform, the 

 navicular, and half the astragalus ; and on its fibular side 

 the fourth digit and metatarsal, the cuboid and the«other 

 half of the astragalus. The distal articular surface of the 



