DISSECTION OP THE POSTEEIOE LIMB. 71 



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 muscido- 

 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 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 1 8, 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 supracondyloid 

 fossa of the femur, the inner head from the supracondyloid crest. The 

 cord-like tendon is joined by that of the soletis, and is inserted into the 

 back part of the summit of the os calcis. When the hock is strongly flexed, 

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

 of the siimmit, 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. 



The SoLBTJS (Plate 18). In British veterinary text-books this muscle 

 is erroneously termed plantaris. It is a small muscle of delicate 

 texture, and it is often partially or entirely removed in cleaning the 



