THE POSTERIOR TIBIO-FIBULAR REGION. 



439 



' Femur. 



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. The grooves in the astragalus and os calcis, which 

 contain the tendon of the muscle, are converted by tendi- 

 nous fibres into distinct canals lined by synovial membrane ; 

 and as the tendon crosses the sole of the foot, it is con- 

 nected to the common flexor by a tendinous slip. 



Relations. By its superficial 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 (perforans) 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 posterior sur- 

 face of the muscle. This tendon passes behind the internal 

 malleolus in a groove, common to it and the Tibialis pos- 

 ticus, 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 the foot (Fig. 262), where, cross- 

 ing superficially to the tendon of the Flexor longus hal- 

 lucis, 1 to which it is connected by a strong tendinous slip, 

 it becomes expanded, is joined by the Flexor accessorius, 

 and finally divides into four tendons which are inserted 

 into the bases of the last phalanges of the four lesser toes, 

 each tendon passing through a fissure in the tendon of the 

 Flexor brevis digitorum opposite the base of the first 

 phalanges. 



Relations. In the leg : by its superficial surface, 

 with the posterior tibial vessels and nerve, and the deep 

 transverse fascia, which separates it from the Soleus 

 muscle ; by its deep surface, with the Tibia and Tibialis 

 posticus. In the foot it is covered by the Abductor 

 hallucis and Flexor brevis digitorum, and crosses superfi- 

 cial to the Flexor longus hallucis. 



The Tibialis posticus lies between the two preceding 

 muscles, and is the most deeply seated of all the muscles 

 in the leg. It commences above by two pointed processes, 

 separated by an angular interval, through which the an- 

 terior tibial vessels pass forward to the front of the leg. It arises from the whole of 

 the posterior surface of the interosseous membrane, excepting its lowest part, from 

 the outer portion of the posterior surface of the shaft of the tibia, between the 

 1 That is, in the order of dissection of the sole of the foot. 



FIG. 260. Muscles of the 

 back of the leg. Deep layer. 



