534 THE MUSCLES AND FASCIAE 



leg, but below, where it covers the tendons passing behind the malleoli, it is thick- 

 ened and continuous with the internal annular ligament. 



This fascia should now be removed, commencing from below opposite the tendons, and 

 detaching it from the muscles in the direction of their fibres. 



The Popliteus (m. popliteus) (Fig. 391) is a thin, flat, triangular muscle, which 

 forms part of the floor of the popliteal space. It arises by a strong tendon, about 

 an inch in length, from a deep depression on the outer side of the external condyle 

 of the femur, and from the posterior ligament of the knee-joint. The muscle is 

 inserted into the inner two-thirds of the triangular surface above the oblique line 

 on the posterior surface of the shaft of the tibia, and into the tendinous expansion 

 covering the surface of the muscle. The tendon of the muscle is covered by that 

 of the Biceps femoris and by the external lateral ligament of the knee-joint; it 

 grooves the posterior border of the external semilunar fibrocartilage, and is invested 

 by the synovial membrane of the knee-joint. 



Relations. By its superficial surface, with the fascia covering it, which separates it from 

 the Gastrocnemius, Plantaris, popliteal vessels, and internal popliteal nerve; by its deep surface, 

 with the knee-joint and back of the tibia. 



The Flexor longus hallucis (m. flexor hallucis longus} is situated on the fibular 

 side of the leg, and is the most superficial and largest of the three next muscles. 

 It arises from the lower two-thirds of the posterior surface of the shaft of the 

 fibula, with the exception of an inch at its lowest part; from the lower part of 

 the interosseous membrane; from an intermuscular septum between it and the 

 Peronei, externally; and from the fascia covering the Tibialis posticus internally. 

 The fibres pass obliquely downward and backward, and terminate in a tendon 

 which occupies nearly the whole length of the posterior surface of the muscle. 

 This tendon occupies a groove on the posterior surface of the lower end of the 

 tibia; it then lies in a second groove on the posterior surface of the astragalus, and 

 finally in a third groove, beneath the sustentaculum tali of the os calcis, and 

 passes into the sole of the foot, where it runs forward between the two heads of 

 the Flexor brevis hallucis, and is inserted into the base of the last phalanx of the 

 great toe (Fig. 399). The grooves in the astragalus and os calcis, which contain 

 the tendon of the muscle, are converted by tendinous fibres into distinct canals 

 lined by synovial membrane; and as the tendon crosses the sole of the foot, it is 

 connected to the Common Flexor by a tendinous slip. 



Relations. By its super/idol surface, with the Soleus and tendo Achillis, from which it is 

 separated by the deep transverse fascia ; by its deep surface, with the fibula, Tibialis posticus, 

 the peroneal vessels, the lower part of the interosseous membrane, and the ankle-joint; by its 

 outer border, with the Peronei; by its inner border, with the Tibialis posticus and posterior tibial 

 vessels and nerve. In the sole of the foot it lies above the Abductor hallucis and Flexor longus 

 digitorum. 



The Flexor longus digitorum (m. flexor digitorum longus} is situated on the 

 tibial side of the leg. At its origin it is thin and pointed, but gradually increases 

 in size as it descends. It arises from the posterior surface of the shaft of the tibia, 

 immediately below the oblique line to within three inches of its extremity, internal 

 to the tibial origin of the Tibialis posticus; some fibres also arise from the fascia 

 covering the Tibialis posticus. The fibres terminate in a tendon which runs nearly 

 the whole length of the superficial surface of the muscle. This tendon passes 

 behind the internal malleolus in a groove, common to it and the Tibialis posticus, 

 but separated from the latter by a fibrous septum, each tendon being contained 

 in a special sheath lined by a separate synovial membrane. It then passes obliquely 

 forward and outward, superficial to the internal lateral ligament, into the sole of 



