XIX.] 



UNGULATA. 



j~> 



Various gradational stages between the complete tridac- 

 tyle foot of the Rhinoceros and the monodactyle foot of 

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

 dactyla. 



In the Artiodactyla 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 



a. 



mUT 



FIG. 126. Dorsal surface of right tarsu- 

 of Rhinoceros {Rhinoceros suinatrcn- 

 sis). i. 



FIG. 127. Dorsal surface of right tarsus 

 of Horse (guus caballus), j. 



symmetrical form. The second and fifth toes, when present 

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

 through 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 



