SKELETON OF ARTIODACTYLA. 



457 



and the Ruminants. The bones of the foot are described at 

 p. 308, fig. 193 (Horse). 



The astragalus shows the extreme perissodactyle modification 

 by the depth and obliquity of the superior trochlea, and by the 

 extensive and undivided anterior surface, which is almost entirely 

 appropriated by the naviculare : the ectocuneiforme, which is the 

 homotype of the magnum in the carpus, is equally remarkable for 

 its large size, since it supports that metatarsal, answering to the 

 middle one in pentadactyle quadrupeds, which constitutes the 

 chief part of the hind-foot in the Horse. 



§ 188. Skeleton of Artiodactyla, — Some of the common osteo- 

 logical characters of this order, with the genera representing it, 

 are given at pp. 285, 286. 



A. Vertebral Column. — In the Hippopotamus, fig. 306, the 



306 



Eip-popotamus amphibius. 



vertebral formula is : — 7 cervical, 15 dorsal, 4 lumbar, 6 sacral, 

 16 caudal. The pleurapophysial parts of the transverse processes 

 of the third to the sixth cervical inclusive develope hatchet- 

 shaped plates, progressively increasing in size, which overlap each 

 other. The second and third cervical s have bituberculate hypa- 

 pophyses. The transverse processes of all the cervicals are per- 

 forated by the vertebral arteries. The neural spines elongate 

 from the third to the seventh cervical, C. Six pairs of ribs 

 directly join the sternum, which consists of five bones and a 

 broad ensiform cartilage. A metapo})hysial ridge is developed 

 above the diapophyses of the eighth dorsal, changes its position 

 and shape with increase of size in the two succeeding vertebras, 

 in the eleventh projects forward from above the prozygapophysis. 



