THE POSTERIOR CRURAL MUSCLES 485 



the floor of the popliteal fossa. It arises by a strong tendon about 2.5 cm. long, 

 from a depression at the anterior part of the groove on the lateral condyle of the 

 femur, and to a small extent from the oblique popliteal ligament of the knee-joint; 

 and is inserted into the medial two-thirds of the triangular surface above the pop- 

 liteal line on the posterior surface of the body of the tibia, and into the tendinous 

 expansion covering the surface of the muscle. 



I Variations. Additional head from the sesamoid bone in the outer head of the Gastrocnemius. 

 Popliteus minor, rare, origin from femur on the inner side of the Plantaris, insertion into the pos- 

 terior ligament of the knee-joint. Peroneotibialis, 14 per cent., origin inner side of the head of the 

 fibula, insertion into the upper end of the oblique line of the tibia, it lies beneath the Popliteus. 



The Flexor hallucis longus is situated on the fibular side of the leg. It arises 

 from the inferior two-thirds of the posterior surface of the body of the fibula, with 

 the exception of 2.5 cm. at its lowest part; from the lower part of the interosseous 

 membrane; from an intermuscular septum between it and the Peronsei, laterally, 

 and from the fascia covering the Tibialis posterior, medially. The fibers pass 

 obliquely downward and backward, and end in a tendon which occupies nearly 

 the whole length of the posterior surface of the muscle. This tendon lies in a groove 

 which crosses the posterior surface of the lower end of the tibia, the posterior 

 surface of the talus, and the under surface of the sustentaculum tali of the calca- 

 neus; in the sole of the foot it runs forward between the two heads of the Flexor 

 hallucis brevis, and is inserted into the base of the last phalanx of the great toe. 

 The grooves on the talus and calcaneus, which contain the tendon of the muscle, 

 are converted by tendinous fibers into distinct canals, lined by a mucous sheath. 

 As the tendon passes forward in the sole of the foot, it is situated above, and 

 crosses from the lateral to the medial side of the tendon of the Flexor digitorum 

 longus, to which it is connected by a fibrous slip. 



Variations. t'sually a slip runs to the Flexor digitorum and frequently an additional slip runs 

 froin the Flexor digitorum to the Flexor hallucis. Peroneocalcaneus internus, rare, origin below 

 or outside the Flexor hallucis from the back of the fibula, passes over the sustentaculum tali with 

 he Flexor hallucis and is inserted into the calcaneum. 



< 



The Flexor digitorum longus is situated on the tibial side of the leg. At its 

 origin it is thin and pointed, but it gradually increases in size as it descends. It 

 arises from the posterior surface of the body of the tibia, from immediately below 

 the popliteal line to within 7 or 8 cm. of its lower extremity, medial to the tibial 

 origin of the Tibialis posterior; it also arises from the fascia covering the Tibialis 

 posterior. The fibers end in a tendon, which runs nearly the whole length of the 

 posterior surface of the muscle. This tendon passes behind the medial malleolus, 

 in a groove, common to it and the Tibialis posterior, but separated from the latter 

 by a fibrous septum, each tendon being contained in a special compartment lined 

 by a separate mucous sheath. It passes obliquely forward and lateralward, super- 

 ficial to the deltoid ligament of the ankle-joint, into the sole of the foot (Fig. 444), 

 where it crosses below the tendon of the Flexor hallucis longus, and receives from it 

 a strong tendinous slip. It then expands and is joined by the Quadratus plantse, 

 and finally divides into four tendons, which are inserted into the bases of the last 

 phalanges of the second, third, fourth, and fifth toes, each tendon passing through 

 an opening in the corresponding tendon of the Flexor digitorum brevis opposite 

 the base of the first phalanx. 



Variations. Flexor accessorius longus digitorum, not infrequent, origin from fibula, or tibia, 

 or the deep fascia and ending in a tendon which, after passing beneath the laciniate ligament, 

 joins the tendon of the long flexor or the Quadratus piantse. 



The Tibialis posterior ( Tibialis posticus] lies between the two preceding muscles, 

 and is the most deeply seated of the muscles on the back of the leg. It begins 

 above by two pointed processes, separated by an angular interval through which 



