490 



THE MUSCULATURE 





1 



flexor longus tendon perforates as it passes to the base of the terminal phalanx. The tendon 

 is connected, hke those of the fingers, by vincula tendinum, to the phalanges of the toes. 



Nerve-supply. — From the tibial (posterior tibial) nerve a branch arises, often in company 

 with nerves to some other or others of the muscles of this group. The nerve divides into two 

 branches, one of which passes to the lateral side of the muscle, where it extends along near the 

 middle of the fibre-bundles of that side, while the other branch passes along near the middle 

 of the fibre-bundles of the medial side of the muscle. 



Relations. — In the proximal half of the leg it lies on the tibia, in the distal half on the 

 posterior tibial muscle. Between it and the flexor hallucis lie the posterior tibial vessels and 

 nerve. Near the ankle the plantar vessels and nerves cross the tendon of the muscle, separated 

 from it by the deep layer of the laciniate (internal annular) ligament. In the upper two-thirds 

 of its extent it is covered by the triceps surse. In the lower third of the leg it emerges medial to 

 the soleus and the tendon of Achilles. The relations of its tendon at the ankle have been de- 

 scribed above. The tendon hes beneath the origin of the abductor hallucis muscle and in the 

 sole is covered by the flexor digitorum brevis, crosses the tendon of the long flexor and the 

 obhque adductor of the big toe and the interosseous muscles, is joined by the quadratus plantae 

 (flexor accessorius), and gives origin to the lumbrical muscles. 



The flexor hallucis longus (figs. 416, 420). — Origin. — From the distal two-thirds of the 

 posterior surface of the fibula, the septa between it and the tibiaUs posterior and peroneal 

 muscles, and the fascia above its proximal extremity. 



Structure and insertion. — The fibre-bundles converge upon a tendon which begins in the 

 second quarter of the muscle, within its substance, and emerges upon the postero-medial margin 

 in its distal half. The insertion of the fibre-bundles continues to the end of the tibia. From 

 here the tendon passes over the dorsal talo-tibial (tibio-astragaloid) ligament, and through the 

 groove on the posterior surface of the talus and the under surface of the sustentaculum tah, 

 where it hes on the fibular side of the tendon of the flexor digitorum longus. It then crosses 

 the deep surface of this tendon, to which it gives a slip, passes over the plantar surface of the 

 medial head of the flexor hallucis brevis, and between the sesamoid bones of this muscle into 

 the osteo-fibrous canal on the plantar surface of the big toe. It is inserted into the base of 

 the terminal phalanx of the big toe. 



Nerve-supply. — The nerve arises from the tibial (posterior tibial) nerve, often in company 

 with the nerve to the flexor digitorum longus or the other muscles of the group. It runs 

 along the deep surface of the muscle and sends twigs into the middle third of its constituent 

 fibre-bundles. Sometimes two nerves are furnished to the muscle. 



Relations. — It lies on the fibular side of the distal two-thirds of the leg. Proximally it 



diverges from the preceding muscle so as to disclose the tibialis posterior, which is more deeply 



situated. Between it and the tibialis posterior lie the peroneal vessels. Distally its tibial 



S margin approaches the flexor digitorum longus, but between them lie the posterior tibial vessels 



^A^ . and nerve. Lateral to it lie the peroneal muscles. It is covered in the leg by the soleus. In 



''^ y the distal part of the leg its tendon hes medial to the tendon of AchiUes. On entering the foot 



>L^ ^ the tendon crosses beneath the abductor hallucis muscle and the lateral plantar vessels and 



<^ ^ nerve. The other relations of the tendon have been described above. 



y <aJ The tibialis posterior (figs. 416, 422). — Origin. — From — (1) the lateral half of the distal 



"^ 7 margin of the popliteal fine and the middle third of the posterior surface of the tibia; (2) the 

 •v^^ medial side of the head and of that part of the body of the fibula next the interosseous mem- 

 brane in the proximal two-thirds; (3) from the whole of the proximal and the lateral portion of 

 the distal part of the posterior surface of the interosseous membrane; and (4) from the septa 

 between its proximal portion and the long flexor muscles. 



Structure. — From this extensive area of origin the fibre-bundles converge upon a tendon 

 which is at first deep seated within the muscle-belly, but about the middle of the leg emerges 

 on the medial margin of the muscle. The fibular portion of the muscle is much more extensive 

 than the tibial. The proximal fibres take a nearly perpendicular, the most distal (from 

 the fibula) a nearly transverse, course. The insertion of fibres stops a little proximal to 

 the medial malleolus. The tendon then extends to the medial side of the tendon of the long 

 flexor of the toes, passes through the groove on the back of the malleolus, across the medial 

 talo-tibial (tibio-astragaloid) ligament, and above the sustentaculum tah to the sole. 



Insertion. — The tendon divides into two chief divisions, a deep and a superficial. (1) 

 The deep portion becomes attached chiefly to the tubercle of the navicular bone, and usually 

 in part also to the first cuneiform. (2) The superficial spreads out to be attached chiefly to the 

 third cuneiform and the base of the fourth metatarsal, but also in part to the second cuneiform, 

 to the capsule of the naviculo-cuneiform joint, to the sulcus of the cuboid, and usually also to 

 -) ^ the origin of the short flexor of the big toe and the base of the second metatarsal. Slips may, 

 J •- J however, also be given to other structures. A sesamoid bone is usually found in the tendon 

 J either near the calcanco-navicular ligament or the navicular bone. 



' 4>. Nerm-.snpply. — The nerve arises from the til)ial (posterior tibial) in company often with 



C^ca^, branches to the other muscles of the group. It enters the posterior surface of the muscle in its 



. proximal third, and gives olT one or two branches for the tibial fasciculus. The main trunk 



V ^'descends across the middle third of the fasciculi arising from the fibula. 



^ J" Relations. — The muscle covers the posterior surface of the interosseous membrane, and 



extends distally over the posterior surface of the til)ia beneath the flexor digitorum longus. It 



is covered proximally by the soleus, distally by the two long digital flexors. The posterior 



rY.^bial and peroneal arteries and the tibial (posterior tibial) nerve run upon its posterior surface. 



J The tenrion in the sole is under cover of the origin of the plantar muscles of the big toe. 



w Action. — The tibialis posterior adducfs the foot and slightly inverts it. The flexor digi- 



,1 . tonmi longus flexes the terminal phalanx on the second and the second on the first, and at the 



J height of its contraction the first on the metatarsals. It also rotates medially to some extent 



• a the ends of the fourth and fifth toes, and inverts the fqpt. The f^or hallucis longus flexes 







