MUSCLES OF GREAT TOE 495 



b. Muscles Attached to the Tendons of the Flexor Digitorum 



LoNGUS (fig. 420) 



The muscles belonging in this group are the quadratus plantse (flexor ac- 

 cessorius), a flat, quadrangular, bicipital muscle which runs from the medial and 

 plantar surface of the body of the calcaneus to the dorso-lateral margin and deep 

 surface of the long flexor tendon; and the lumbricales, four slender bipinnate 

 muscles which run from the medial sides of the digital slips of the tendon to the 

 medial sides of the four more lateral toes. The quadratus aids the long flexor 

 muscle; the lumbricales extend the last two phalanges and flex the first phalanx 

 of each of the digits to which they pass. The lumbrical muscles correspond to 

 those of the hand. The quadratus is not there represented. The nerve-supply 

 is from the lateral (external) plantar nerve except that for the first lumbrical 

 muscle which gets its supply from the medial (internal) plantar. 



The quadratus plantae (flexor accessorius) (fig. 420). — This muscle arises by two heads- 

 The lateral head springs by an elongated tendon from the calcaneus in front of the lateral 

 process of the tuber, and from the lateral margin of the long plantar hgament. The viedial head 

 arises directly from the medial surface of the body of the calcaneus as far back as the medial 

 process of the tuber calcanei, and from neighbouring hgaments. 



Structure and insertion. — The two heads are separated at their origin by a short triangular 

 space. They soon fuse to form a single belly, but the fibre-bundles of each head in the main 

 are separately inserted. Those from the lateral head diverge to be attached to the lateral 

 margin of the flexor tendon. Those from the medial head are inserted on a tendon that begins 

 on the medial margin and deep surface of this head, becomes broader, and is inserted as a 

 flat aponeurosis on the deep surface of the flexor tendon. There are great individual varia- 

 tions in the structure of this muscle. The fibres of either part may be inserted with those of 

 the other part. 



Nerve-supply. — From a branch of the lateral plantar nerve which passes obUquely across 

 the superficial surface of the muscle parallel with the tendon of the flexor digitorum longus. 



Relations. — The muscle hes in a fascial compartment with the long flexor tendons. This 

 compartment is bounded on each side by intermuscular septa, deeply by the tarsus, and plantar- 

 ward by a septum which intervenes between it and the flexor digitorum brevis, and in which the 

 lateral plantar nerve and vessels cross to the lateral side of the foot. 



Action. — It assists the long flexor tendon in flexing the toes. It makes the direction of 

 traction on the toes parallel with the long axis of the foot. 



Variations. — It is frequently reduced in size. The lateral head is not infrequently missing, 

 the medial head or the whole muscle much more rarely. The mode of attachment to the tendon 

 varies. It may be inserted in part or wholly into the long flexor of the great toe. It may 

 receive, in about one body in twenty (Wood), an accessory slip of origin from the fibula, one of 

 the muscles of the leg, the fascia of the leg or foot, or the medial surface of the calcaneus, etc. 



The lumbricales. — The three lateral muscles arise from the contiguous sides of the digital 

 tendon-slips of the flexor digitorum longus in the angles of division. The first lumbrical arises 

 on the medial margin of the tendon to the second toe. The fibre-bundles of each muscle con- 

 verge on both sides of a tendon which becomes free near the metatarso-phalangeal joint and is 

 attached to the medial side of the first phalanx of the toe to which the muscle belongs. A tendi- 

 nous expansion is sent into the aponeurosis of the extensor muscle. 



Nerve-supply. — The three lateral lumbrical muscles are most frequently suppHed by 

 branches of the deep ramus of the lateral plantar nerve, the medial by the first common plantar 

 digital branch of the medial plantar nerve. The latter nerve may supply the two more medial 

 muscles or the more medial muscles may receive a double supplJ^ The branches of the lateral 

 plantar nerve enter the deep surfaces of the muscles in the middle third. The branches of the 

 medial plantar enter the medial borders of the muscles near the junction of the proximal and 

 middle thirds. 



Relations. — The lumbrical muscles He in a plane with the long flexor tendons deeper than 

 the flexor brevis tendons and superficial to the adductor hallucis. The deep branches of the 

 lateral plantar nerve and vessels pass across their deep surface; superficial branches of both 

 plantar nerves across the superficial surface. 



Action. — To extend the last two phalanges of the toes and to flex the first. 



Variations. — One or more of the muscles may be absent. Sometimes a muscle is doubled. 

 This is more frequently the case with the third and fourth muscles. The first may arise 

 wholly from the tendon of the posterior tibial muscle or from this and the long flexor of the 

 big toe. The third lumbrical may arise from the flexor die:itorum brevis. The second and 

 fourth lumbricals may be inserted into the tendons of the flexor digitorum brevis. 



c. Intrinsic Muscles of the Great Toe (figs. 419-421) 



These muscles are the abductor, flexor brevis, and adductor. Of the three 

 muscles, the first two lie in the medial fascial compartment, while the last lies in 

 the middle compartment covered by the flexor digitorum longus and its associated 

 muscles. 



