486 THE MUSCULATURE 



or semimembranosus, from the linea aspera, or popliteal space may join the triceps and give 

 rise to a quadriceps supjb. On the other hand, one of the heads of the gastrocnemius or the 

 tibial head of the soleus may be missing. A supernumerary fasciculus may extend from the 

 deep surface of the soleus to the calcaneus. The plantaris is exceedingly variable in origin, 

 structure, and insertion. The origin may be from the capsule of the knee-joint, the fascia of the 

 leg, or from the tibia. Its tendon may terminate at almost any part of its course in neighbouring 

 structures. It may be represented by a fibrous band. It is absent in about 7 per cent, of 

 instances (Le Double). 



BURSiE 



B. m. gastrocnemii lateralis. — A bursa is often found between the tendon of the lateral 

 head of the gastrocnemius and the capsule of the joint. It may communicate with the joint 

 cavity. B. m. gastrocnemii medialis. — A bursa usually lies between the tendon of origin of 

 the medial head of the gastrocnemius, the condyle of the humerus, and the capsule of the joint. 

 Another bursa (b. m. semimembranosi) extends between the semimembranosus and the medial 

 head of the gastrocnemius muscle. The two bursae frequently communicate with one another 

 and with the joint. B. tendinis calcanei. — This lies between the tendon of Achilles and the 

 upper part of the back of the calcaneus. Between the back of the tendon and the crural fascia 

 another bursa is frequently present. 



h. Deep Group 



The deep posterior musculature is separated from the superficial by the trans- 

 verse septum described above (p. 479). The muscles covered by this septal fascia 

 are the popliteus, the flexor digitorum longus, the flexor hallucis longus, and 

 the tibialis posterior. An intermuscular septum between the popliteus and the 

 tibialis posterior, and the attachment of the soleus to the popliteal line on the 

 back of the tibia serve to separate the popliteus from the other deep posterior 

 muscles which He distal to this region and send tendons into the sole of the foot 

 The deep posterior musculature may thus be considered as divided into a proximal 

 femoro-tibial and a distal cruro-pedal group. Both sets of muscles are supplied 

 by branches of the tibial nerve. 



Femoro-tibial Muscle 



The popliteus (fig. 416). — A triangular muscle which arises from an ovoid 

 facet at the inferior extremity of the groove on the outer side of the lateral condyle 

 of the femur and is inserted into the proximal lip of the popliteal line of the tibia 

 and the surface of the shaft of the tibia proximal to this. It rotates the leg 

 medialward and flexes it. 



Structure. — From the origin a broad tendon ghdes over the condyle within the capsule of 

 the joint, then over the lateral fibro-cartilage and through a groove on the back of the tibio-fibu- 

 lar articulation. From both surfaces of this tendon, fibre-bundles diverge toward the area of 

 insertion. The tendon is more or less intimately united to several structures with which it 

 comes in contact about the joint. Rarely it contains a sesamoid bone. The fibres of insertion 

 terminate in part in the fascia covering the muscle. The pophteus is homologous with the 

 pronator teres of the arm, or, according to some investigators, with the deep portion of that 

 muscle. 



Nerve-supply. — A nerve which arises either independently or in conjunction with that to 

 the posterior tibial muscle enters the popliteus near the middle of its distal edge. Sometimes 

 a branch from the chief nerve to the knee-joint enters the proximal edge of the muscle. 



Action. — To flex and rotate the leg medially. 



Relations. — The popliteus lies within a compartment bounded by the transverse septum, 

 the capsules of the knee and superior tibio-fibular joints, the back of the tibia, and a septum 

 extending to the popliteal line (see above). On the transverse septum run the popliteal vessels 

 and the tibial nerve. The proximal margin of the soleus overlaps the distal margin of the 

 popliteus. The synovial membrane of the knee-joint sends a prolongation between its tendon 

 and the back of the lateral condyle of the tibia. 



Variations. — It is rarely absent. An accessory head may arise from the medial side of 

 the lateral condyle or from some neighbouring structure. The fibulo-tibialis (peroneo-tibialis) 

 is a small muscle found by Gruber in one body in seven. It arises from the medial side of the 

 head of the fibula and is mserted into the posterior surface of the tibia beneath the pophteus. 



Cruro-pedal Muscles (figs. 416, 420) 



Of the three muscles of this group, the flexor digitorum longus lies on the 

 tibial sido of the leg, the flexor hallucis longus on the fibular side, and the tibialis 

 posterior upon the intorossoous membrane, partly covered by the other two 



J 



