THE MUSCLES ON THE POSTEKIOK ASPECT OF THE LEG. 431 



The lumbrical muscles have a similar action to those of the hand ; they flex the metatarso- 

 phalangeal, and extend the interphalangeal joints of the four lateral toes. 



M. Quadratus Plantae. The quadratus plantae (O.T. accessorial) arises by two 

 heads : (1) the lateral tendinous head springs from the lateral border of the plantar 

 surface of the calcaneus and from the lateral border of the long plantar ligament ; 

 (2) the medial head, which is fleshy, arises from the concave medial surface of the 

 calcaneus in its whole extent, and from the medial border of the long plantar 

 ligament (Fig. 379, p. 425). The long plantar ligament separates the two origins. 



The two heads unite to form a flattened band, which is inserted into the dorsal 

 aspects of the tendons of the flexor digitorum longus, and usually into those 

 destined for the second, third, and fourth toes. 



In the sole of the foot the tendons of the flexor digitorum longus, along with the 

 lumbricales and quadratus plantse, and the flexor hallucis longus muscles, constitute 

 the second layer of muscles, lying between the abductors of the great and little toes 

 and the flexor digitorum brevis superficially, and the flexor brevis and adductor of 

 the great toe more deeply. 



Nerve-Supply. Lateral plantar nerve (S. 1. 2.). 



Actions. The muscle is an accessory flexor of the toes, assisting the long flexor of the toes. 

 It tends to draw the tendons into which it is inserted into the middle of the sole of the foot. 



M. Flexor Hallucis Longus. The flexor hallucis longus arises, on the back 

 of the leg, between the tibialis posterior and the peronsei muscles, from the distal 

 two-thirds of the posterior surface of the body of the fibula, from the fascia over 

 it, and from intermuscular septa on either side. 



Its tendon passes deep to the ligamentum laciniatum, enclosed in a special 



mucous sheath, and after grooving the posterior surface of the distal end of the 



* tibia, the talus, and the plantar surface of the sustentaculum tali of the calcaneus, 



it is directed forwards in the sole of the foot, to be inserted into the base of the 



terminal phalanx of the great toe. 



In the foot it crosses over the deep aspect of the tendon of the flexor digitorum 

 longus, and gives to it a strong fibrous slip, which is prolonged into the tendons for 

 the second and third toes. 



Nerve-Supply. Tibial nerve (L. 5. S. 1. 2.). 



Actions. The muscle is one of the most important in the leg and foot. It is an extensor of 

 the ankle and a flexor of the great toe. By its position in relation to the tarsus and inferior 

 ft calcaneo-navicular ligament, it has an important share in maintaining and supporting the arch 

 1 of the foot. 



M. Tibialis Posterior. The tibialis posterior has a fourfold fleshy origin in 



I the leg. It arises (1) from the proximal four-fifths of the medial surface of the 



I body of the fibula between the medial crest and the interosseous crest ; (2) from 



> the distal part of the lateral condyle, and from the proximal two-thirds of the 



body of the tibia, distal to the oblique line and between the vertical line and the 



interosseous border (Fig. 384, p. 428) ; (3) from the interosseous membrane ; and 



(4) from the fascia over it and the septa on either side. The muscle gives rise to 



a strong tendon which passes deep to the ligamentum laciniatum, invested by a 



special mucous sheath, and grooves the back of the medial malleolus, on its way 



to the medial border of the foot. 



After crossing over the plantar calcaneo-navicular ligament between the 

 sustentaculurn tali and the navicular bone, the tendon spreads out and is inserted 

 by three bands into (1) the tubercle of the navicular bone and the plantar surfaces 

 of the first and second cuneiform bones, (2) the plantar aspects of the bases of the 

 second, third, fourth, and sometimes the fifth metatarsal bones, the second and 

 third cuneiform bones, and the groove on the cuboid, and (3) into the medial 

 border of the sustentaculum tali of the calcaneus (Fig. 379, p. 425). 



The peronaeo-calcaneus muscle, when present, arises from the fibula, and is inserted into the 

 calcaneus. 



Nerve-Supply. Tibial nerve (L. 5. S. 1.). 



Actions. The muscle extends the ankle and inverts the foot. 



