744 



THE UNGULATES, OR HOOFED MAMMALS 



FOOT 

 HORSE. 



of the others, the third and fourth toes become symmetrical to a vertical line drawn 

 between them. When this takes place the first toe disappears, and the second and 

 fifth become diminished in size; an instance of this stage of development being 

 presented by the pig, where the two large and medially-symmetrical 

 toes represent the third and fourth of the typical series, while the two 

 small lateral ones are the second and fifth. In the pigs* all the met- 

 acarpal bones remain distinct and relatively short; but in the water- 

 chevrotain * of Africa the third and fourth metacarpals become much 

 elongated and closely applied to one another, while the second and 

 fifth are reduced to mere splints, and their toes so diminished as 

 to become practically functionless. Finally, in the deer, oxen, and 

 their allies, the third and fourth metacarpals in the fore-limb, and 

 the corresponding metatarsal bones in the hind-limb, have become com- 

 BONESOFFORE- pletely fused into a single rod-like bone, corresponding in function 

 OF with the canon bone of the horse, and generally known by the same 

 name. The dual origin of this canon bone is, however, proclaimed 

 by the formation of its lower extremity, which carries two pulley-like surfaces, with 



which the bones of the two functional toes (the third and 

 fourth) articulate. 



Since all the Ungulates displaying this second modi- 

 fication of foot structure agree in having the third and 

 fourth toes arranged symmetrically to a line drawn be- 

 tween them, they are collectively termed the Kven-Toed 

 Ungulates. 



It is accordingly evident that although a few living 

 Ungulates, like the elephant and the hyrax, retain a gen- 

 eralized type of foot, the greater number of the living 

 representatives of the order are characterized by their 

 more or less markedly specialized feet. 



As regards their teeth, the Ungulates are 

 characterized by those of the cheek series 

 having broad crowns, surmounted either by columns or 

 transverse ridges, and adapted for grinding and masti- 

 cating vegetable substances. In the more specialized 

 forms, like cattle and horses, these cheek-teeth have their 

 columns or ridges of great height and closely approxi- 

 mated to one another, in consequence of which the bases 

 of the hollows, or valleys by which these columns or 

 ridges are separated from one another, cannot be seen 

 when the tooth is unworn; while the pattern produced 

 on the crown by the wearing down of these columns or 



HIND-FEET OF AN EX- ridges is complex. On the other hand, in the more prim- 

 itive tyP es > sucn as pig s and tapirs, the crowns of the 



Teeth 



BONES OF THE FORE AND 



* Figures of the bones of the feet of these animals are given under their respective headings. 



