494 



THE MUSCULATURE 



The nerve supply is from 



sublimis is supposed to be represented by the soleus. 

 the medial (internal) plantar. 



Origin. — From (1) the medial process of the tuber calcanei; (2) the posterior third of the 

 plantar aponeurosis; and (3) the medial and lateral intermuscular septa. 



Structure. — The constituent fibre-bundles pass distally in a compact mass. The tendons 

 of insertion begin within the muscle substance, and as the fibre-bundles become inserted on 

 them, the separate fascicuh become more and more distinct. The fascicuh for the second and 

 third toes are larger and arise more superficially than those for the fourth and fifth toes. The 

 fasciculus for the fifth toe is often very small, and its tendon takes an obhque course to the 

 insertion. 



Insertion. — The tendons of the short flexor pass superficial to those of the long flexor into 

 the osteo-fibrous canals on the flexor surface of the digits. Upon the first phalanx of each toe 

 the tendon of the short flexor divides and forms an opening (chiasma tendinis) through which 



Fig. 419. — First Later of the Muscles of the Sole 



Abductor digiti V 



Flexor digiti V brevis 



Tendon of flexor digitorumlongus 



Flexor digitorum brevis 



Abductor hallucis 



Flexor hallucis longus 



Flexor hallucis brevis 

 First lumbrical 



-Tendon of adductor hallucis 



^■l 



4 



i 



the tendon of the long flexor passes, while the tendon of the short flexor becomes attached to the 

 base of the second phalanx. The arrangement is essentially like that described at length for 

 the flexors of the fingers (p. 401). 



Nerve-supply. — From the medial plantar nerve by a branch which enters the middle third 

 of the deep surface near the medial margin of the muscle. 



Action. — It is a strong flexor of the second row of phalanges. 



Relations. — The short flexor is separated from the abductors of the big toe and little toe 

 bv strong intermuscular septa (p. 492), and from the long flexor tendons and the quadratus 

 planta; (flexor accessorius) by a transverse septum in which the lateral plantar vessels and 

 nerve cross the foot. In its distal two-thirds it is separated from the plantar fascia by loose 

 tissue. 



Variations. — The muscle shows a tendency toward reduction, one or more of its fasciculi 

 being frequently absent, and occasionally the whole muscle. The fasciculus for the fifth toe 

 is absent in about 20 per cent, of bodies (Le Double). When a fasciculus is absent, its tendon is 

 u.sually replaced by an accessory tendon from Ihe long flexor. The muscle or its tendons may 

 be more or less fused to the tendons of the flexor digitorum longus. 



