76 THE ANATOMY OF THE HORSE. 



brings it into company with the terminal part of the posterior tibial 

 nerve ; and, passing with that nerve into the tarsal sheath, it divides at 

 the back of the hock into the two plantar arteries. The collateral 

 branches of the posterior tibial are — (1) muscular branches to the deep 

 muscles at the back of the leg ; (2) the nutrient artery of the tibia ; (3) 

 a retrograde branch which, emanating from the second curve of the 

 sigmoid flexure, ascends in front of the tendo AchiUis ; (4) articular 

 branches to the tarsus. 



Veins. The foregoing arteries run in company with satellite veins 

 bearing the same names. 



Directions. — The front of the leg must now be dissected ; and, as 

 the first step, the muscles of the region should be cleaned and isolated. 

 These are — the extensor pedis, the flexor metatarsi, and the peroneus. 

 The first of these is superposed to the second on the front of the leg, 

 while to the outer side of both is the smaller peroneus. In dissecting 

 the tendons of these muscles in the region of the hock, care should be 

 taken of three transverse fibrous bands that retain the tendons in 

 position (Plates 18 and 19). The first of these bands is fixed by its 

 extremities to the lower end of the tibia, and beneath it pass the 

 tendons of the extensor pedis and flexor metatarsi. The second is 

 fixed outwardly to os calcis ; and, passing over the extensor pedis 

 tendon, it is attached to the flexor metatarsi. The third retains the 

 tendons of the extensor pedis and peroneus in position at the upper end 

 of the large metatarsal bone, to which its extremities are attached. 



The Extensor Pedis (Plate 18). This muscle arises, in common with 

 the tendinous portion of the flexor metatarsi (Fig. 3, page 77), from the 

 pit between the trochlea and external condyle of the femur. It has a 

 thick, fusiform muscular belly, which at the lower third of the leg is 

 succeeded by a strong tendon. This passes over the front of the hock, 

 and under the three annular bands just described. It then descends 

 over the front of the metatarsus, where it receives the insertion of the 

 short extensor of the digit, and is joined by the tendon of the peroneus. 

 In the dissection of the digit it will be pursued to its insertion into the 

 pyramidal eminence of the os pedis. 



Action. — It extends in succession from below upwards the interphalan- 

 geal joints and the fetlock, and finally flexes the hock. 



The Peroneus (Plate 18). This is a much smaller muscle than the 

 preceding, to whose outer side it lies. Its muscular fibres have a penni- 

 form arrangement, and arise from the external lateral ligament of the 

 stifle, from the fibula, and from the aponeurotic septum between it and 

 the deep flexor of the phalanges. Its tendon passes through the groove 

 on the external tuberosity (external malleolus) at the lower end of the 

 tibia, and then over the outer side of the hock, where it plays in a 

 synovial canal formed in the external lateral ligament. Below the 



