382 THE MUSCLES 



2. THE FOUR LUMBRICALES 



The four lumbricales — named from their shape (lumbrirus = an earthworm) — 

 are, like those in the pahn, four small fusiform muscles. 



Origin. — The tirst, from the inner l)order of the innermost tendon of the flexor 

 lonj2;us di^dtorum, from the point of division of the main tendon for al)out an inch 

 (•2-5em. ) forwards; the other three, from the adjacent surfaces of the first and 

 second, tlie second and third, and the third and fourth tendons of the flexor longus 

 digitorum on their plantar aspect. 



Insertion. — The inner Iwrder of the expansion of the extensor longus digitorum 

 tendon u}>on the hack of the tirst phalanx of each of the four outer toes. 



Structure. — The origin of the muscle is entirely fleshy. It ends in a small 

 rounded tendon a short distance ahove the web of the toes. This tendon runs 

 forwards and upwards upon the inner side of its toe, above the superficial transverse 

 ligament of the toes and beneath the deep transverse ligament of the metatarsus, 

 to the side of the expansion of the extensor tendon. 



Nerve-supply. — The innermost is supplied by the internal jdantar division 

 of the posterior tilnal nerve, by filaments which enter the back part of the lower 

 surface of the muscle near its inner border; the three outer, by the external 

 plantar nerve, by filaments which enter the deep part of each muscle near its 

 outer border. 

 " Action. — (1) To flex the first phalanx of the toe; (2) to straighten the second 

 and third phalanges. (3) The first will abduct the second toe from the axis 

 passing through it, which is looked upon as the middle line of the foot. The three 

 others will adduct. The lumljricales will be al)le to act upon the first ithalanges, 

 even Avhen the second and third have been flexed 1)y means of their special flexors. 

 The chief advantage derived from the simultaneous extension of the two terminal 

 phalanges and the flexion of tlie first phalanx is the application of the whole length 

 of the toe to the ground in walking; otherwise there would be a strong tendency 

 to the flexion of the phalanges of the toes, which would prevent the proper appli- 

 cation of the soft plantar aspect of the ungual phalanx to the ground. 



Relations. — Superficially, the flexor brevis digitorum. Deeply, the flexor 

 longus digitorum tendons, the transversalis pedis, and the interossei. 



Third Layer 



The third layer consists of four muscles — the flexor brevis hallucis, the adductor 

 hallucis, the transversus pedis, and the flexor brevis minimi digiti. 



1. FLEXOR BREVIS HALLUCIS 



The flexor brevis hallucis, or flexor brevis pollicis pedis — named from its 

 action, and its size in comparison Avith the other flexor of the great toe — is a thick 

 triangular sheet with a forked insertion. 



Origin. — { 1) The ])lantar ligaments and the continuations of the tibialis 

 posticus tendon in the middle of the solo; (2) the inner part of the under surface 

 of the cuboid bone. 



Insertion. — The inner and outer borders of the jdantar aspect of the base of the 

 first phalanx of the great toe. 



Structure. — Arising fibrous by a pointed ])rocess in the middle of the sole, the 

 fibr(>s diverge as they pass forwards and slightly iuAvards, and form two fleshy 

 bundles of eipial size, which are succeeded liy short tendons. In each tendon is 

 contained a sesamoid l)one of ovoid shape about three-eigliths of an inch (1 cm.) in 

 the long antero-])osterior diameter, and a quarter of an inch (7 nun.) from side to 

 side, Avith a cartilaginous articular facet U])on tlie ui)i)er surface Avhich ))lays U])on 

 the lower surface of the coiidvle of the first metatarsal bone. At their insertion 



