394 THE INFERIOR EXTREMITY 



M. Quadratus Plants (O.T. Flexor Accessorius). This 

 muscle takes a course straight forwards from the heel, and 

 acts as a direct flexor of the toes. It also tends to bring the 

 tendons of the long flexor muscle into a line with the toes upon 

 which they operate. It arises by two heads which embrace 

 the calcaneus and the long plantar ligament. The medial 

 head, wide and fleshy, springs from the medial concave 

 surface of the calcaneus ; the lateral head, narrow, pointed, 

 and tendinous, takes origin from the lateral surface of the 

 calcaneus, and also from the long plantar ligament. The 

 quadratus plantse is inserted into the tendon of the flexor 

 digitorum longus in the middle of the sole. It is supplied 

 by a branch from the lateral plantar nerve. 



Mm. Lumbricales. The lumbrical muscles of the foot are 

 not so strong as the corresponding muscles in the palm of the 

 hand. They are four in number, and arise from the tendons 

 of the flexor digitorum longus. The lateral three lumbricals 

 spring from the adjacent sides of the tendons between which 

 they lie ; the first or most medial muscle takes origin from the 

 medial side of the tendon of the long flexor which goes to the 

 second toe. The slender tendons of the lumbrical muscles 

 proceed to the medial sides of the lateral four toes, and are 

 inserted into the expansions of the extensor tendons on the 

 dorsal aspects of the proximal phalanges (see p. 346). The 

 first or most medial lumbrical is supplied by the medial plantar 

 nerve : the others are supplied by the lateral plantar nerve. 



Dissection. To bring the third layer of muscles into view 

 the following dissection must be made : Divide the two heads 

 of the quadratus plantae and draw the muscle forwards from 

 under the lateral plantar vessels and nerve. Sever also the 

 tendons of the flexor digitorum longus and the flexor hallucis 

 longus at the point where they emerge from under cover of the 

 ligamentum laciniatum, and turn them towards the toes, after 

 cutting the branch from the lateral plantar nerve to the quadratus 

 plantae. As the tendons of the long flexor of the toes are turned 

 forwards the lumbrical muscles will be raised, and the twigs which 

 are furnished to the second, third, and fourth by the deep division 

 of the lateral plantar nerve must be looked for. That for the 

 second lumbrical muscle will be seen to take a recurrent course 

 round the transverse head of the adductor hallucis muscle. 

 Lastly, cut the medial plantar nerve close to its origin and turn 

 it aside. 



Third Layer of Muscles. The flexor hallucis brevis lies 

 along the lateral side of the abductor hallucis. 



The oblique head of the adductor hallucis has a very oblique 



