754 



Comparative Morphology of Chordates 



Rhinocebotidae : Three digits on manus, three on pes. One or two 

 median "horns" on forepart of head (Fig. 566). Unlike horns of other 

 ungulates, the rhinoceros horn is composed of longitudinal fibers of 

 horny substance and has no bony core, being probably a mass of fused 

 hairs. The rhinoceroses occur in Asia and Africa. 



Distribution of Perissodactyla. Modern Equidae are native to 

 the Eastern Hemisphere only, but fossil remains of members of all 

 three modern Families of Perissodactyla are found in the Western 



Fig. 567. Peccary, Dicotyles. (Courtesy, Flower 

 and Lydekker: "Introduction to the Study of Mam- 

 mals," London, A. & C. Black, Ltd.) 



Hemisphere, including a complete series of progressively equine mam- 

 mals which were quite clearly ancestral to the modern horse. 



Order 14: ARTIODACTYLA. "Even-toed" or paraxonic. The 



axis of symmetry of the foot lies between the third and fourth digits 

 (Fig. 564), which are equally and symmetrically developed and func- 

 tionally most important. The other digits are reduced or absent. If 

 present, the second and fifth are symmetrically developed. The first 

 occurred in some extinct artiodact \ Is. 



The dentition is of the herbivorous type — cutting incisors; canines 

 usually small, sometimes lacking; cheek-teeth usually grinders. 



Two Suborders are distinguished: 



Suborder SUINA (BUNODONTIA). Four digits on each foot, 

 the second and fifth being fairly well-developed. Canine teeth become 



