66o 



HUMAN ANATOMY. 



(aa) The Muscles of the First Layer. 



1. Flexor brevis digitorum. 3. Abductor hallucis. 



2. Flexor brevis hallucis. 4. Abductor minimi digiti. 



I. Flexor Brevis Digitorum (Fig. 627). 



Attachments. — The short flexor of the toes (m. flexor digitorum brevis) arises 

 from the inner process of the calcaneal tuberosity and from the plantar aponeurosis. 

 It extends distally, beneath the aponeurosis, as a thick quadrangular muscle, the 



fibres of which are collected 



Fig. 627. 



/ 



Os calcis - 



Abductor hallucis 



Flexor brevis 

 digitorum 



Flexor brevis 

 hallucis 



Flexor longus 

 hallucis tendon 



over the metatarsal bones 

 into four tendons which pass 

 to the second, third, fourth, 

 and fifth toes. Over the 

 first phalanx of the toe each 

 tendon divides into two ter- 

 minal slips, between which 

 the corresponding tendon of 

 the flexor longus digitorum 

 passes and which are zn- 

 se^ted into the second pha- 

 lanx. 



Nerve-Supply. — By 

 the internal plantar nerve 

 from the fourth and fifth 

 lumbar and first sacral 

 nerves. 



Action. — To flex the 

 second, third, fourth, and 



Flexor brevis fifth tOeS. 

 mmimi digiti 



Abductor 

 minimi digiti 



Flexor longus 

 -digitorum ten- 

 dons 



Flexor brevis 

 digitorum ten- 

 dons 



Flexor tendons 

 in sheath 



Flex. brev. digi- 

 torum tendon 



Flexor longus digitorum 

 tendon 



Superficial muscles of sole of right foot. 



Variations.— The most fre- 

 quent variation in this muscle is 

 the absence of the tendon to 

 the fifth toe, an absence which 

 occurs in somew hat o\er 21 per 

 cent, of cases examined. Some- 

 times the tendon is replaced by 

 a slip or muscle which arises 

 from the tendon of the flexor 

 longus digitorum. 



The flexor brevis repre- 

 sents the middle portion of the 

 superficial flexor layer, and cor- 

 responds, accordingly, to the 

 terminal portions of the ten- 

 dons of the flexor sublimis of 

 the hand. Its origin is primarily 

 from the plantar aponeurosis, 

 and hence the occasional origin 

 of the portion for the fifth toe 

 becomes intelligible, since the 

 tendon of the flexor longus is 

 a differentiation of the deeper 

 layer of the aponeurosis. 



2. Flexor Brevis Hallucis (Fig. 628). 



Attachments. — The short flexor of the great toe (m. flexor hallucis brevis) 

 arises from the plantar surface of the internal cuneiform bone and the adjacent liga- 

 mentous structures. Its fibres pass distally to a tendon which contains a sesamoid 

 bone, and is inserted into the inner surface of the base of the first phalanx of the 

 great toe. 



Nerve-Supply. — By the internal plantar nerve from the fourth lumbar nerve. 



Action. — To flex the great toe. 



