DISSECTION OF THE POSTERIOR LIMB. 75 



back of the leg ; (2) the mitrient artery of the tibia ; (3) a retrograde 

 branch which, emanating from the second curve of the sigmoid flexure, 

 ascends in front of the tendo Achillis ; (4) articidar branches to the tarsus. 



Veins. The foregoing arteries run in company with satellite veins 

 bearing the same names. 



Directions. — The front of the leg mvist 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 posi- 

 tion (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 ex- 

 tensor 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 76), from the pit 

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

 fusiform mviscular 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 dissec- 

 tion of the digit it Avill 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 

 hock it is directed obliquely forward, and joins the tendon of the extensor 

 pedis about the middle of the metatarsus. 



Action. — The same as the preceding muscle. 



Directions. — Cut the extensor pedis about tlie middle of the leg, and 

 reflect it upwards and downwards to expose the next muscle. 



