72 THE ANATOMY OP THE HORSE. 



Cutaneous Nerves. 1. The ramifications of the internal saphenous 

 uerve 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, 

 Avhere 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 semitendiuosus 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 meta- 

 tarsal region. 



Directions. — The muscles on the back of the leg may now be dissected, 

 the vessels and nerves shown in Plates 17 and 18 being at the same 

 time carefully preserved. By a reference to Plate 18, the student should 

 note the position of the small soleus 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 calois. 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 

 Achillis. 



Action. — To extend the hock-joint. 



