THE CRURAL MUSCLES. 651 



Action. — To assist in extending the foot and to tense the crural fascia at the 

 ankle-joint. 



Variations. — The plantaris is absent in about 7 per cent, of cases. Its insertion may be 

 into the calcaneum, the tendo AchilHs, the crural fascia, or even into the plantar aponeurosis. 



{bb) The Middle Layer. 

 I. Flexor longus digitorum. 2. Flexor longus hallucis. 



I. Flexor Longu5 Digitorum (Figs. 620, 628). 



Attachments. — The long flexor of the toes (m. flexor digitorum longus) arises 

 from almost the whole of the posterior surface of the tibia below the oblique line and 

 from the deep surface of the deep layer of the crural fascia. Its fibres converge in a 

 bipinnate manner to a tendon which passes laterally to the tendon of the tibialis 

 anticus beneath the internal annular ligament, and so reaches the plantar region of 

 the foot. There it is directed somewhat laterally, receiving the insertion of the flexor 

 accessorius, and divides into four tendons which, passing through the divided ten- 

 dons of the flexor brevis, are inserted into the base of the third or distal phalanx of 

 the second, third, fourth, and fifth toes. 



Nerve-Supply. — By the posterior tibial nerve from the fifth lumbar and first 

 sacral nerves. 



Action. — To flex the second, third, fourth, and fifth toes ; continuing its action, 

 to extend the foot and to cause slight inversion of the sole. 



Relations. — In the leg (Fig. 617) the flexor longus is covered by the soleus 

 and has resting upon it the lower portions of the posterior tibial vessels and nerve. 

 It rests upon the tibialis posticus, crossing it obliquely in the lower part of the leg. 

 In the foot its tendons are covered by the flexor brevis digitorum, and pass between 

 the two terminal slips of the tendons of that muscle over the first phalanges. Its 

 tendon is also covered by the abductor hallucis, and crosses obliquely the tendon of 

 the flexor longus hallucis and the oblique portion of the adductor hallucis. The 

 lumbricales take their origin from its tendons, and it receives the insertion of the 

 flexor accessorius. 



Variations. — A flexor digitorum longus accessorius is occasionally found arising indepen- 

 dently from the tibia or from the fibula and joining the tendon of the long flexor below, or else 

 uniting with the flexor accessorius. 



2. Flexor Longus Hallucis (Figs. 620, 628). 



Attachments. — The long flexor of the great toe (m. flexor hallucis longus) arises 

 from the posterior surface of the fibula, from the posterior intermuscular septum, 

 and from the deep surface of the deep layer of the crural fascia. Its fibres converge 

 bipinnately to a tendon which passes beneath the internal annular ligament, pos- 

 terior to the posterior tibial vessels and nerve, and so enters the plantar surface 

 of the foot. There it passes beneath the tendon of the flexor longus digitorum, 

 to which it sends a slip, and continues distally to be inserted into the base of the 

 distal phalanx of the great toe, passing between the flexor brevis hallucis and the 

 first plantar interosseous. 



Nerve-Supply. — By the posterior tibial nerve from the fourth and fifth lumbar 

 and first sacral nerves. 



Action. — To flex the hallux and extend and slightly supinate the foot. 



Variations. — The principal variations of the flexor longus hallucis concern its union with 

 the tendon of the flexor longus digitorum. The passage of a slip between the two tendons is 

 constant, but its distribution to the tendons of the flexor digitorum varies considerably. Usually 

 it separates into two slips which pass to the tendons for the second and third toes, but it may also 

 pass to the tendons for the second, third, and fourth toes, to that of the second alone, or even 

 to all the tendons of the flexor longus digitorum. It may also completely replace the tendon 

 usually passing from the flexor longus digitorum to the second digit. 



