FLEXOR LONGUS HALLUCIS. T1BIALIS POSTICTJS. 267 



of the astragalus and the under surface of the sustentaculum tali, being bound down 

 to those bones by a fibrous sheath lined by synovial membrane. Thence passing 

 forwards and inwards in the sole of the foot, it gives off a slip to the tendon of the 

 flexor longus digitorum, by which it is crossed, and proceeds in a fibrous sheath 

 over the first phalanx of the great toe to be inserted into the base of the terminal 

 phalanx. 



Relations. This muscle is concealed for the most part by the soleus, a small part only on 

 the outer side of the tendo Achillis being- covered by the fascia of the leg. Externally it is in 

 contact with the peronei, and internally with the posterior tibial vessels and nerve. It rests 

 upon the fibula and tibialis posticus. and conceals the peroneal vessels. Behind the ankle the 

 tendon of this muscle is separated from that of the flexor longus digitorum by an interval of 

 more than half an inch, in which are placed the posterior tibial vessels and nerve. In the 

 sole it is covered by the abductor hallucis and the plantar fascia ; it is also crossed by the 

 plantar vessels and nerves as well as by the tendon of the long flexor of the toes. It rests 

 upon the flexor brevis hallucis. 



Varieties. This muscle is liable to very few variations, except in the mode of union of its 

 tendon with that of the flexor longus digitorum which is exceedingly variable. In almost 

 every case a slip is given from the flexor hallucis to the flexor digitorum ; and frequently (1 

 in 5) an additional slip proceeds from the flexor digitorum to the flexor hallucis. Complete 

 separation of the tendons is very rare. This slip from the flexor hallucis most frequently 

 passes to the second and third toes (52 per cent.), but it may pass to the second only (28 per 

 cent.), or to the second, third and fourth (19 per cent.), or rarely to all the four outer toes. 



The peroneo-calcaneus internus is a rare muscle, which arises below or outside the flexor 

 longus hallucis from the back of the fibula, and passes over the sustentaculum tali in the 

 groove with the flexor hallucis to be inserted into the os calcis. 



The tibialis posticus muscle, placed beneath the two long flexor muscles, arises 

 from the posterior surface of the interosseous membrane, from the outer portion 

 of the posterior surface of the tibia, extending from the superior tibio-fibular 

 articulation to the middle of the bone, from the whole inner surface of the fibula, and 

 slightly from the aponeurosis covering it. The fleshy fibres pass to a tendon which, 

 commencing above in the centre of the muscle, descends along its inner border, 

 becomes free at the level of the lower tibio-fibular articulation, and gains the 

 groove at the back of the internal malleolus, where it is contained in a fibrous 

 sheath and surrounded by synovial membrane. It then inclines forwards and ends 

 by being inserted into the tuberosity of the navicular bone, sending offsets forwards 

 to the three cuneiform bones, to the cuboid, and to the bases of the second, third 

 and fourth metatarsal bones, as well as a thin process backwards to the sustenta- 

 culum tali. Near its insertion the tendon contains a sesamoid fibro-cartilage, 

 occasionally a bone, as it lies over the head of the astragalus. 



Relations. The posterior surface of the tibialis posticus is in contact with the long 

 flexors of the toes and the posterior tibial and peroneal vessels, while at the upper end the 

 anterior tibial vessels are directed forwards between its attachments to the two bones. In the 

 lower part of the leg the muscle crosses obliquely inwards beneath the flexor longus digitorum, 

 and its tendon becomes superficial for a short distance, lying close to the hinder border of the 

 internal malleolus. In the foot it is covered by the abductor hallucis, and it rests against the 

 internal calcaneo-navicular ligament which separates it from the head of the astragalus. 



Varieties. These are rare. An additional muscle has been seen occasionally arising from 

 the back of the tibia below the flexor digitorum, and inserted into the capsule of the ankle- 

 joint or into the annular ligament. This is the tensor of the capmle of the ankle-joint of 

 Henle and Linhart, or the tibialis sccundus of Bahnsen. 



Nerves. The gastrocnemius, plantaris and popliteus are supplied by the internal popliteal 

 nerve. The soleus receives one branch from the internal popliteal nerve and another from the 

 posterior tibial. The flexor longus digitorum, flexor longus hallucis and tibialis posticus 

 derive their nerves from the posterior tibial. 



