POSTERIOR LIMB 17 



side for the rudimentary metatarsal. It is supposed that the 

 small metacarpal and metatarsal bones are merely survivals in 

 the process of evolution, and that in the primitive animals from 

 which the modern horse is descended these bones were larger 

 than they are now, having the same length and the same func- 

 tional importance as the principal metacarpal and metatarsal 

 bones. The original ancestor of the horse is supposed to have 

 had five metacarpals and five metatarsals with corresponding 

 digits or toes, and to have walked on five toes instead of one. 



The horse has three phalanges and the cow six. These bones 

 are closely similar to the phalanges of the front pastern. They 

 are commonly known as the first, second and third phalanges, 

 or os suffraginis, os corona, and os pedis. 



The sesamoids and navicular bones are very similar to the 

 corresponding bones of the front limb already described. Ani- 

 mal-husbandry students should find the application of preced- 

 ing lessons helpful by giving a clear view of the anatomical 

 basis of conformation, type and action. 



Practical application. — Note how the external angle of the 

 ilium fixes the "roughness" or "smoothness" of the hips; how 

 the length and slope of the femur fixes the length and slope of 

 the thigh, and controls the action of the limb, for example the 

 cow and hog have comparatively horizontal femurs and are 

 awkward travelers. Note the tibia in its relation to length and 

 slope of the leg or gaskin, or lower thigh, as this region is vari- 

 ously named, and how this affects the stride of the roadster. 



The tarsal bones make the framework and determine largely 

 the conformation and strength of the hock. 



Whether the point of the hock is prominent or otherwise de- 

 pends on the os calcis, one of the tarsal bones. Good hock action 

 depends to an important extent upon the peculiar oblique articu- 

 lar surfaces of the astragalus and tibia. The principal meta- 

 tarsal determines the length of the cannon, and this in turn 

 affects the stride of the roadster and the power of the draft 

 horse. 



Length and slope of the pastern depends on length and slope 

 and articulations of the first and second phalanges and these 

 give elastic spring or jar and cause the horse to go clear or 

 interfere at the ankle. 



Disorders of the posterior limb are even more numerous than 

 those of the fore limb. The three pelvic bones are all subject 



