MUSCLES OF THE SOLE 



493 



Nerve-supply. — The deep peroneal (anterior tibial) nerve, which, accompanied by the 

 anterior tibial artery, passes beneath the medial belly of the muscle, gives off a branch which 

 passes transversely across the middle of the deep surface of the muscle and sends twigs into it. 



Relations. — It lies on the lateral side of the tarsus, beneath the long extensor tendons of the 

 toes. The relations of its tendons have been described above. 



Action. — It aids the long extensors in extending the first phalanx of each of the four medial 

 digits. It has but a limited action on the second and third phalanges. It serves also to pull 

 the ends of the toes to which its tendons go toward the little toe. 



Fig. 418. — The Muscle of the Dorsum of the Foot. 



Transverse crural ligament 



Extensor digitorum longus — j- -^ 



Tibialis anterior 



Extensor digitorum brevis 



Extensor hallucis longus 



Dorsal interossei «r-^^^ 



Peroneus brevis 



Cruciate ligament 



Peroneus tertius 



Flexor digiti V brevis 



Variations. — The muscle shows great variation in development. Rarely the whole muscle, 

 more frequently one or more of its digital divisions, may be missing. On the other hand, it may 

 be more highly developed than usual. Accessory fascicuh vary greatly in origin and termi- 

 nation. Most frequently their tendons go to a metacarpo-phalangeal articulation or to the 

 second or the fifth toe. 



2. Muscles of the Sole of the Foot 

 a. Flexor Digitorum Brevis (fig. 419) 



The flexor digitorum brevis, the most superficially placed of the plantar 

 muscles, lies in the mid-plantar region beneath the plantar fascia and over the 

 tendons of the long flexor of the toes and its associated muscles. It arises from 

 the calcaneus, and has a flat, elongated belly, which toward the middle of the sole 

 is prolonged into four processes, each of which has a special tendon that is inserted 

 into the second phalanx of one of the four lateral toes. The tendons of the muscle 

 correspond to those of the flexor sublimis in the palm. The belly of the flexor 



I 



