154 



UNGULATES. 



BONES OF FORE- 

 FOOT OF HORSE. 



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 1 

 all the metacarpal bones remain distinct and relatively short ; but 

 in the water -chevrotain 1 of Africa the third and fourth meta- 

 carpals 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 completely fused into a single rod-like bone, 

 corresponding in function with the cannon-bone of the horse, and 

 generally known by the same name. The dual origin of this 

 cannon-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 

 between them, they are collectively termed the Even- 

 Toed Ungulates. 



It is accordingly evident that although a few living 

 Ungulates, like the elephant and the hyrax, retain a 

 generalised type of foot, the greater number of the 

 living representatives of the order are characterised by 

 their more or less markedly specialised feet. 



As regards their teeth, the Ungulates 

 are characterised by those of the cheek- 

 series having broad crowns, surmounted either by columns 

 or transverse ridges, and adapted for grinding and 

 masticating vegetable substances. In the more specialised 

 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 

 ridges is complex. On the other hand, in the more 

 primitive types, such as pigs and tapirs, the crowns of the 

 cheek-teeth have low columns, or ridges, so that the bases 

 of the intervening valleys can be distinctly seen at all 



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



Teeth. 



BONES OF THE FORE AND HIND 

 FEET OF AN EXTINCT DEER 



— After Osborn. 



