THE LOWER LIMB 



499 



form two distinct fibrous sheaths for the peroneal tendons, which 

 are here lying one above the other (the peroneus brevis tendon 

 being the upper one) as they traverse the outer surface of the os 

 calcis. Each tendon has now its own synovial investment, the 

 common synovial sheath beneath the external annular ligament 

 having sent forward two prolongations. 



The internal annular ligament is chiefly formed by a thicken- 

 ing of the posterior or transverse intermuscular septum, but super- 

 ficial to it there is also the proper deep fascia, though that is here 

 very thin. This annular ligament extends between the posterior 

 border of the internal malleolus and the internal border of the tuber 

 calcis, and is directed downwards and backwards. Its upper 

 border is continuous principally with the posterior intermuscular 



Tibialis Posticus -,. 

 Flexor Longus Digitorum 



Posterior Tibial Artery and Vense Comites ^ Pt.~-- 



Posterior Tibial Nerve 



Flexor Longus Hallucis 



Plantaris 



Abductor Hallucis 



Internal Annular Ligament 



Fig. 240. — The Structures between the Internal Malleolus 

 AND the Heel. 



septum. Its lower border gives origin on its deep aspect to the 

 inner head of the abductor hallucis, and on its superficial aspect 

 it is in part continuous with the lower limb of the Y division 

 of the anterior annular ligament. The internal annular ligament 

 passes over the grooves on the back of the lower end of 

 the tibia, and converts these into canals for the flexor tendons and 

 posterior tibial vessels and nerve. There are in all four canals, 

 three of them being fibro-osseous and one fibrous. The relation of 

 structures beneath this ligament, from the internal malleolus 

 outwards to the tuber calcis, is as follows : (i) the tendon of the 

 tibialis posticus, lying in the groove behind the internal malleolus 

 close to the bone, and occupying one of the fibro-osseous canals ; (2) 

 the tendon of the flexor longus digitorum, lying behind, and 

 slightly external to, that of the tibialis posticus, and occupying the 



