616 



COMPARATIVE PHYSIOLOaY. 



in which the toes end, are not only weapons of offense and de- 

 fense, but protective against injury from contact with hard sur- 

 faces, as well as directly helpful in locomotion. These princ 

 pies are admirably exemplified in the foot of soUpeds. 



The foot of the horse may be said to consist of terminal 

 bones incased in soft structures adapted to shield the animal 

 from the effects of excessive concussion and for nutrition, the 



FiQ. 459. 



Fig. 460. 



Pig. 459.— Longitudinal median section of foot. 1, anterior extensor of phalanges, 

 or extensor pedis; 2, lateral extensor, or extensor siifflraginis; 3, capsule of meta- 

 carpo-phalangeal articulation; 4. large metacarpal bone; 5, superficial flexor of 

 phalanges, orperforatus: 6, deep flexor, or perforans: 7, sheath-; 8, bursa; 9, sesa- 

 moid bone: 10, ergot and fatty cushion of fetlock; 11, crucial Mgament; 12, short 

 sesamoid ligament; 13, first phalanx; 14, bursa; 15, second .phalanx; 16, navicu- 

 lar bone; 17, plantar cushion; 18, third phalanx; 19, plantar surface of hoof; 20, 

 sensitive or keratogenons membrane of third phalanx. 



Fig. 460.— Horizontal section of horse's foot. 1, front or toe of hoof; 2, thickness of 

 wall; 3, lamina; 4, insertion of extensor pedis; 5, os pedis; 6, navicular bone; 7, 

 wings of OS pedis; 8, lateral cartilage; 9, flexor pedis tendon; 10, plantar cushion; 

 11, inflexion of wall or *'bar"; 12, nomy frog. 



whole being' incased in a protective covering which in a state 

 of nature is constantly being worn away and renewed. The 

 hoof is the homologue of the nails and claws of other mammals, 

 and so may be regarded as a modification of the epidermis; 

 and thus viewed, its structure is at once more readily under- 

 stood and more interesting. To speak from an anatomical 

 standpoint, the foot of the' horse is made up of the terminal 



