72 THE ANATOMY OF THE HORSE. 



. Cutaneous Nerves. 1. The ramifications of the internal saphenous 

 nerve cover the inside of the leg, and descend over the inside of the 

 hock. 2. The external saphenous nerve (Plate 18) is a branch of the 

 great sciatic. It descends over the outer head of the gastrocnemius, 

 where it is covered by the biceps, and is reinforced by a branch from 

 the external popliteal (or from the peroneal cutaneous division of that 

 nerve). It then continues to descend, lying in company with the 

 vein of the same name, in front of the outer edge of the gastrocnemius 

 tendon ; and, passing over the hock, it is" distributed to the' skin on 

 the outer side of the metatarsus. 3. The cutaneous termination of 

 the musculo-cutaneous division of the external popliteal nerve (Plate 18) 

 pierces the deep fascia on the outer side of the limb at the lower 

 third of the leg; and, passing over the hock, it is distributed to the 

 skin on the front of the metatarsus. 



Deep Fascia of the Leg. This forms a close-fitting fibrous 

 envelope to the muscles of the region. Its inner face furnishes septa 

 that pass in between the muscles, and over the inner surface and crest 

 of the tibia it is adherent to the bone. Above it is continuous with 

 the fascia lata and tendons of the gracilis and semitendinosus on the 

 inside, and with the tendon of the biceps on the outside. As it passes 

 over the hock it becomes thinner, and is continuous with the fascia of 

 the metatarsal region. 



Directions. — The muscles on the back of the leg may now be dis- 

 sected, the vessels and nerves shown in Plates 17 and 18 being at 

 the same time carefully preserved. By a refererice to Plate 18, the 

 student should note the position of the small soletis muscle, so as to 

 avoid its removal with the fascia. 



The Gastrocnemius (Plates 17 and 18). At its origin this muscle 

 consists of two distinct fleshy heads, which terminate in a single 

 inferior tendon. The outer head arises from the outer lip of the supra- 

 condyloid fossa of the femur, the inner head from the supracondyloid 

 crest. The cord-like tendon is joined by that of the soleus, and is 

 inserted into the summit of the tuber calcis. When the hock is strongly 

 flexed, the tendon for an inch or two above its insertion rests on the 

 forepart of the summit, and a small synovial bursa is here interposed 

 between the tendon and the bone. The tendon of the perforatus is at 

 first beneath that of the gastrocnemius ; but, passing to the inner side, 

 it places itself superficial to the latter, which it completely covers at the 

 summit of the os calcis. In thus changing positions, the two tendons 

 form a half twist, and indent each other like the strands of a rope. 

 This tendon of the gastrocnemius corresponds to the firm tendon 

 extending upwards from the human heel, and known as the tendo 

 A chillis. 



Action. — To extend the hock-joint. 



