SUPERFICIAL EXTENSORS OF ANKLE. 609 



TENDO ACHILLIS (fig. 208, p ). The common tendon of the gastro- 

 cnemius and soleus is one of the strongest in the body. About three 

 inches wide above, it commences at the middle of the leg, though it re- 

 ceives fleshy fibres on the under surface nearly to the lower end : below it 

 is narrowed, and is inserted into the lower half of the tuber calcis at the 

 posterior aspect. A bursa intervenes between it and the upper part of 

 the tuberosity. The tendon is close beneath the fascia ; and lying along 

 its outer side, but superficial to it, are the external saphenous vein and 

 nerve. 



Action. In its action on the foot the soleus, like the gastrocnemius, 

 extends the ankle and points the toes when the foot is free to move, and 

 raises the heel if the toes rest on the ground. By the sudden and power- 

 ful contraction of the fibres of both muscles, the common tendon is 

 sometimes broken across. 



If it acts from the os calcis, it will draw back the bones of the leg into 

 a. vertical position over the foot, as the body is raised to the erect posture 

 after stooping. 



The PLANTARIS (fig. 208, c ) is remarkable in having the longest tendon 

 in the body, which takes the appearance of a ribbon when it is stretched 

 laterally. About three-quarters of an inch wide, the muscle arises from 

 the line above the outer condyle of the femur, and from the posterior 

 ligament of the knee-joint ; and the tendon is inserted into the os calcis 

 with or by the side of the tendo Achillis, or into the fascia of the leg. 



The belly of the muscle, about three inches in length, is concealed by 

 the gastrocnemius, but the tendon appears on the inner side of the tendo 

 Achillis about the middle of the leg. This little muscle crosses the pop- 

 liteal vessels, and lies on the soleus. 



Action. It assists the gastrocnemius to extend the ankle if the foot is 

 not fixed ; and to bend the knee-joint if the foot is immovable. 



Dissection (fig. 209). The soleus is to be detached from the bones of 

 the leg, and the muscles and nerves entering it are to be divided ; but in 

 raising it, the student should take care not to injure the thin deep fascia 

 and the vessels and nerves beneath. The superficial muscles may be next 

 removed by cutting through their tendons near the os calcis ; and the 

 bursa between the tendo Achillis and the os calcis should be opened. 



The piece of fascia between the muscles of the superficial and deep 

 layers is next to be cleaned ; and the integuments between the inner ankle 

 and the heel are to be taken away to lay bare the annular ligament, but a 

 cutaneous nerve to the sole of the foot, which pierces the ligament, is to 

 be preserved. 



Deep part of the fascia. This intermuscular piece of the fascia of the 

 leg is fixed to the tibia and fibula, and binds down the deep layer of flexor 

 muscles. Beneath the soleus it is thin and indistinct ; but lower in the 

 limb it is much stronger, and is marked by some transverse fibres near the 

 malleoli, which gives it the appearance and office of an annular ligament 

 in that situation. Inferiorly it joins the internal annular ligament between 

 the heel and the inner ankle. 



Dissection. The deep layer of muscles (in part), the posterior tibial 

 nerve, and the trunk and offsets of the posterior tibial vessels, will be laid 

 bare by the removal of the fascia and the areolar tissue. A muscle be- 

 tween the bones (tibialis posticus) is partly concealed by an aponeurosis 

 which gives origin to the two muscles (flexor communis and flexor pollicis) 

 39 



