HOOFED ANIMALS 



35 



chestnuts are found above the wrist joint or " knee " ; on the 

 hind-limb they occur below the hock-joint (Fig. 9, C). Until 

 recently their existence was a great puzzle, but it is now held that 

 they are the last remnants of glands which discharged some 

 scented fluid whereby the members of the herd could find 

 one another when separated. They may be likened to dead 

 volcanoes. In asses and zebras the hind callosity is always 

 wanting. But this, it may be remarked, is not the only dis- 

 tinguishing mark between the horse on the one hand, and the 

 asses and zebras on the other. For the first named is peculiar 



FIG. 9. The sole of the foot of a man, a dog, and a horse the latter answering 

 to the " back of the lower part of the leg " to show the pads .described in the 

 text. C, the " chestnut." P, pads. 



in its shorter ears and broader hoofs, and in having the long 

 hairs of the tail continued quite up to its base. 



The remarkably lengthened hand and foot of the horse 

 and this applies also of course to the asses and zebras have 

 been developed in response to the increasing need for speed 

 in flight from enemies, as the ancestral horses in their wandering 

 after food in level and open plains became more and more ex- 

 posed to the attacks of carnivorous foes. All that now remains 

 of the second and fourth digits of the fore- and hind-limbs 

 are slender rod-like bones known as " splints " (Fig. 7, s/>). 

 The oxen, antelopes, and deer, for example, have retained the 

 third and fourth digits as functional members, while the second 



