2 ^6 



FOOT OF UNGULATES 



the liml • passes through the third finger, which is larger than any of 

 the others, and is symmetrical in itself. In this the present group 

 contrasts with the Artiodactyla, where the axis is not " mesaxonic," 

 but where there are two digits, on either side of the axis, which are 

 symmetrical with each other. This arrangement of the limbs is 

 highly characteristic, but appears to be not quite universal. In 

 the Titanotheres, which form a group of the Perissodactyles, the 

 fore-limbs are not quite accurately mesax- 

 onic. Nor on the other hand can all Ungu- 

 lates which show the Perissodactyle condition 

 Ije safely included in the present group. The 

 ancient Condylarthra and the Litopterna 

 show precisely the same state of affairs. 

 But other features in then- organisation lead 

 to their separation from the Perissodactjdes, 

 of which, however, the Condylarthra are 

 probably ancestors. The Litopterna on the 

 other hand, which possess even one -toed 

 members like Equus, are believed to repre- 

 sent a case of parallelism in development. 

 The number of functional toes varies from 

 four to one. In the ankle joint the astra- 

 galus either does not, or does only to a 

 comparatively slight extent, articulate with 

 the cuboid as well as with the navicular 

 of the bone. Moreover the filjula when present 

 does not as a rule articulate with the 

 calcaneum. In the opposed group of 

 Artiodactyles the precise reverse of these 

 ol)tains. It is usually stated 

 as part of the definition of this group 

 that they do not possess horns of the type of those met 

 with in the Cervicornia and Cavicornia. But the strong bony 

 bosses on the skull of many Titanotheres, so curiously remin- 

 iscent of those of the not nearly related Dinoceras and Proto- 

 ceras, may well have supported horns of the Ox and Antelope 

 pattern. 



The teeth of the Perissodactyles are lophodont, more rarely 

 bunodont. The selenodont Artiodactyle form of molar is not 

 ruet with. The dental formula, moreover, is at least near the 



Fig. 122. — Bou. 



mauus of Camel {Camel u.s 



hactriatius). x J. f, 



Cuneiform ; I, lunar ; ta, 



magnum ; iJ, radius ; ^s 



scaphoid ; td, trapezoid ; 



n, unciform.' (From conditions 



Flower's Osteologii. ) 



