EQUIDsE 



393 



but the principal metatarsal is more laterally compressed at its 

 upper end than is the corresponding metacarpal. The joint 

 between the femur and tibia, corresponding to the knee of man, is 

 called the "stifle joint"; while that between the tibia and tarsus, 

 corresponding to the ankle of man, is termed the " hock." The 

 bones and joints of the foot have the same names as in the fore 

 limb. The Horse is eminently " digitigrade," standing 011 the ex- 

 tremity of the single digit of each foot, which is kept habitually in 

 a position approaching to vertical. 



The muscles l of the limbs are modified from those of the ordi- 

 nary mammalian type in accordance with the reduqed condition of 

 the bones and 

 the simple re- 

 quirements of 

 flexion and ex- 

 tension of the 

 joints, no such 

 actions as pro- 

 nation and 

 supination, or 

 opposition of 

 digits, being 

 possible or 

 needed. The 

 muscles, there- 

 fore, which per- 

 f orm these 

 functions in 

 other mammals 

 are absent or 

 rudimentary. 

 . Below..,, the 



FIG. 164. Section of foot of Horse. 1, Metacarpal bone ; 2, first 

 phalanx (os suffraginis); 3, second phalanx (as corona); 4, third or 

 urigual phalanx (os pedis, or coffin-bone) ; 5, one of the upper sesamoid 

 bones; 6, lower sesamoid or "navicular" bone; 7, tendon of anterior 

 Carpal and tar- extensor of the phalanges ; 8, tendon of superficial flexor (fl. perforate) ; 

 9, tendon of deep flexor (fl. perforans) ; 10, suspensory ligament of 

 fetlock ; 11, inferior or short sesamoid ligament ; 12, derma or skin 

 of the foot, covered with hair, and continued into 13, the coronary 

 cushion, 14, the podophyllous or laminar membrane, and 15, the kera- 

 togenous membrane of the sole ; 16, plantar cushion ; 17, hoof; 18, fatty 

 cushion of fetlock. 



sal joints the 

 fore and hind 

 limbs corre- 

 spond almost 

 exactly in struc- 

 ture as well as function. On the anterior or extensor surface of 

 the limb a powerful tendon (7 in Fig. 164), that of the anterior 

 extensor of the phalanges (corresponding to the extensor communis 

 digitorum of the arm and extensor longus digitorum of the foot of man) 

 passes down over the metacarpal bone and phalanges, to be inserted 

 mainly into the upper edge of the anterior surface of the last phalanx 



1 Want of space and of the necessary illustrations rendered it impossible to 

 give an account of mammalian myology in the earlier chapters of this work. 



