THE LOWER LIMB 523 



The greater part of the muscle in the leg is contained in a fibro- 

 osseous canal formed by the posterior or transverse intermuscular 

 septum, the interosseous membrane, the intermuscular septa on 

 either side, and the surfaces of the tibia and fibula from which it 

 arises. 



Flexor Longus Hallucis — Origin. — (i) The lower two-thirds of 

 the posterior surface of the shaft of the fibula, except the last inch 

 or more ; (2) the postero-extemal intermuscular septum, which 

 separates the muscle from the peroneus longus and peroneus 

 brevis ; (3) the intermuscular septum between it and the tibiaUs 

 posticus ; and (4) the posterior or transverse intermuscular septum, 

 as it covers the muscle. 



Insertion. — ^The plantar surface of the base of the distal phalanx 

 of the great toe. 



Nerve-supply. — ^The posterior tibial nerve. 



Action. — (i) The muscle acts as a flexor of the distal phalanx 

 of the great toe ; (2) it is an extensor of the foot upon the leg ; (3) it 

 contributes to the support of the longitudinal arch of the foot ; 

 and (4) by means of the slip which it gives to the tendon of the 

 flexor longus digitorum in the sole it is an auxihary of that 

 muscle, more especially in flexing the second and third toes. 



The tendon passes through the groove on the back of the lower 

 end of the tibia at its outer part, where it lies beneath the internal 

 annular ligament, occupying one of the fibro-osseous canals, and 

 having a special s^niovial investment. Beyond this point it passes 

 in succession through the groove on the posterior border of the 

 astragalus, and through that on the under surface of the sustenta- 

 culum tali of the os calcis. Each of these grooves is converted into 

 a fibro-osseous canal by a fibrous expansion, and in each case the 

 tendon has a synovial investment. In the sole the tendon is crossed 

 superficially or inferiorly, and from within outwards, by that of 

 the flexor longus digitorum, to which it gives a slip. In most 

 cases this slip is incorporated with the long flexor tendons of 

 the second and third toes (Turner). As it passes along the first 

 phalanx it is contained in a fibro-osseous canal lined by synovial 

 membrane, which also invests the tendon and gives rise to a liga- 

 mentum breve. In the leg the flexor longus hallucis is contained 

 within a fibro-osseous canal formed by intermuscular septa and 

 the posterior surface of the shaft of the fibula. 



Posterior Tibial Artery. — ^This vessel is the larger of the two 

 terminal branches of the popliteal, the other being the anterior 

 tibial. It commences at the lower border of the popliteus muscle 

 on a level wi h the lower border of the tubercle of the tibia, 

 fully if inches below the upper surface of the head of that bone, 

 and it terminates at the lower border of the internal annular 

 Hgament by dividing into the internal and external plantar arteries. 

 The termination of the vessel is situated midway between the 

 inner part of the point of the heel and the tip of the internal 

 malleolus. In the upper two- thirds of the leg it is deeply 



