FLEXOR HALLUCIS B REV IS 



497 



annular) ligament; (4) the septum between the muscle and the flexor digitorum brevis; and 

 (5) a fibrous arch which extends on the deep surface of the muscle over the plantar vessels and 

 nerves and the long flexor tendons from the calcaneus to the navicular bone. 



Structure. — From the medial process of the tuber calcanei a tendinous band passes to the 

 deep, lateral side of the muscle. Numerous tendinous bands arise from the other areas of origin. 

 The fibre-bundles arise from these tendons and directly from the fibrous arch. They are 

 attached in a penniform manner to numerous tendinous slips which extend far up in the muscle. 

 These shps become gradually fused into a tendon which appears on the superficial plantar aspect 

 of the muscle. Opposite the distal half of the first metatarsal bone the tendon leaves the 

 belly of the muscle and becomes closely bound to the medial belly of the flexor hallucis brevis. 



Fig. 421. — Third Layer of the Muscles of the Sole. 



Part of abductor digiti V 



Flexor digiti V brevis 



Adductor hallucis (caput 

 transversum) 



Divided tendons of flexor digitorum 

 brevis 



Tendon of flexor digitorum longus. 



Long plantar (long inferior cal- 

 caneo-cuboid) ligament 



Flexor hallucis longus 

 Flexor digitorum longus 

 Tibialis posterior 



— Flexor hallucis brevis 



Adductor hallucis (caput obliquum) 



Tendon of the flexor hallucis 

 longus 



Insertion. — In conjunction with the tendon of the medial belly of the flexor brevis into the 

 base of the first phalanx. It usually sends an expansion to the extensor tendon. 



Nerve-supply. — A branch from the medial plantar nerve usually enters near the middle of 

 the lateral border of the muscle. 



Relations. — It is covered by the plantar fascia and is separated from the muscles of the 

 median compartment by the medial intermuscular septum. It crosses the tendons of the tibialis 

 anterior, tibiaUs posterior, flexor digitorum longus, and flexor hallucis longus muscles and the 

 plantar vessels and nerves. 



The flexor hallucis brevis (fig. 421). — Origin. — From a tendon attached to the first (in- 

 ternal), second and third cuneiform bones. The more lateral of its fibres are continued into 

 the plantar calcaneo-cuboid Ugament and the more medial into the expansion of the tendon of 

 the posterior tibial muscle. 



Structure and insertion. — The fibre-bundles give rise to two belHes, a medial and a lateral. 

 Those of the medial belly pass obliquely medially to be inserted into the tendon of the abductor 

 haUucis, and by a short tendon fused with this into the medial side of the plantar surface of the 

 base of the first phalanx. This tendon contains a sesamoid bone. Those of the lateral converge 

 upon the tendon of the obHque head of the adductor, and the two muscles are inserted by a 

 common tendon, which contains a sesamoid bone, into the lateral side of the plantar surface 

 of the base of the first phalanx. 



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