THE MUSCLES ON THE POSTERIOK ASPECT OF THE LEG. 429 



of the bellies of the gastrociiemius. Prolonged proximally beneath the separate 

 bellies, the tendon forms a broad membranous band connecting together the distal 

 parts of the two bellies. 



Narrowing gradually, and becoming thicker in the distal half of the leg, the 

 tendon is finally inserted into the posterior aspect of the calcaneus. A bursa lies 

 deep to the tendon at its insertion. The tendo calcaneus also affords insertion to 

 the soleus and (sometimes) the plantaris muscles. 



Nerve-Supply. Each head of the muscle is innervated by a branch from the tibial nerve 

 (S. 1. 2.). 



Actions. The muscle is a powerful flexor of the knee and extensor of the ankle. 



M. Plantaris. The plantaris arises by fleshy fibres from the lateral epicondylic 

 line of the femur for about an inch at its distal end, from the adjacent part of the 

 popliteal surface of the femur, and from the oblique ligament of the knee-joint. 



It forms a narrow fleshy slip which ends in a tendon that extends distally in the 

 back of the leg, to be inserted into, the medial side of the tuberosity of the cal- 

 caneus, or the tendo calcaneus, or the ligameutum laciniatum. The tendon of the 

 muscle is capable of considerable lateral extension. 



The plantaris lies between the lateral head of the gastrocnemius and the soleus. 

 In the distal half of the leg its tendon lies along the medial border of the tendo 

 calcaneus. The muscle is not always present. 



Nerve-Supply. Tibial nerve (L. 4. 5. S. 1.). 



Actions. The muscle is an accessory flexor of the knee and extensor of the ankle. 



M. Soleus. The soleus has a triple origin from (1) the posterior surfaces of 

 the head and the proximal third of the body of the fibula; (2) a fibrous arch 

 (arcus tendinous m. solei) stretching, over the popliteal vessels and tifrial nerve, 

 between the tibia and fibula ; and (3) the oblique line, and the middle third of 

 the medial border of the tibia (Fig. 384, p. 428). 



From their origin the proximal muscular fibres are directed distally to join a 

 tendon, placed on the superficial aspect of the muscle, which is inserted into the 

 tendo calcaneus ; the more distal fibres are inserted directly into the tendo calcaneus 

 to within one or two inches of the calcaneus. 



Nerve-Supply. Two nerves supply this muscle. One from the tibial nerve in the popliteal 

 space enters its superficial surface (S. 1. 2.) ; the other from the tibial nerve in the back of the 

 leg supplies the deep surface of the muscle (L. 5. S. 1. 2.). 



Actions. The soleus is a powerful extensor of the ankle. 



The deep muscles of the back of the leg comprise the popliteus, flexor digitorum 

 longus, flexor hallucis longus, and tibialis posterior. 



The popliteus muscle is deeply placed behind the knee-joint, in the floor of the 

 popliteal fossa, and is covered by the popliteal vessels and tibial nerve. The flexor 

 digitorum longus lies behind the tibia, the flexor hallucis longus behind the fibula, 

 and the tibialis posterior, lying between them, is related to the interosseous mem- 

 brane and both bones of the leg. All these muscles are concealed by the superficial 

 group, and are bound down to the bones of the leg by layers of the deep fascia. 



M. Popliteus. The popliteus arises, by a stout tendon, from a rough impression 

 in front of a groove on the lateral aspect of the lateral epicondyle of the femur. 

 The tendon passes between the lateral meniscus and the capsule of the knee-joint, 

 and pierces the posterior ligament, from which it takes an additional fleshy origin. 

 A bursa is placed on the medial side of the tendon, and it usually communicates 

 with the synovial cavity of the knee-joint. 



The muscle is inserted, by fleshy fibres, (1) into a triangular surface on the back 

 of the tibia above the oblique line (Fig. 384, p. 428), and (2) into the fascia over it 

 (the popliteus fascia, derived from the tendon of the semimembranosus muscle). 



The popliteus minor is a small occasional muscle attached to the popliteal surface of the 

 femur and the posterior ligament of the knee-joint. 



Nerve-Supply. The popliteus is supplied by a branch of the tibial nerve (L. 4. 5. S. 1.), 

 which winds round the distal border of the muscle and enters it in its deep surface. 



Actions. A medial rotator of the tibia and flexor of the knee. 



