374 THE MUSCLES 



1. FLEXOR LONGUS DIGITORUM PEDIS 



The flexor longus digitorum — nanu'd from its being the longer of the two 

 flexors of the toes — is a fusiform slieet. 



Origin. — (1) The inner part of the posterior surface of the tibia, beginning with 

 the lower lialf of the oblique line, and ending about three inches (7*5 cm. ) above the 

 inner ankle; (2) the front of the deep fascia Avhich covers the sheet; (3) a thin in- 

 termusi'ular septum which intervenes between this muscle and the tibialis posticus. 



Insertion. — The under surface of the base of the ungual phalanx of each of the 

 four outer toes. 



Structure. — Arising flesh v from the tibia and adjacent fascia?, the fibres pass 

 in a penniform manner into the front and outer side of a tendon which, beginning 

 about the middle of the leg, gradually becomes thicker and stronger, and receives 

 its last fleshy fibres about two inches (5 cm. ) above the ankle-joint. It then 

 passes beneath the internal annular ligament in a compartment posterior and 

 external to that for the tiV)ialis posticus. Thence it runs downwards, forwards, and 

 outwards beneath the first layer of the sole muscles, and, after having received 

 fleshy fibres from the accessorius pedis and a small tendinous slip from the tendon 

 of the flexor longus hallucis, divides, aliout half-way between the tuberosity of the 

 calcaneuin and the heads of the metatarsal bones, into four tendons. These enter 

 the theca? of the four outer toes, and each tendon passes through the splitting of the 

 tendon of the flexor brevis digitorum to its insertion upon the under surface of 

 the base of the third phalanx. The lumbricales arise from its tendons in the sole 

 of tlie foot. 



Nerve-supply. — From the posterior tibial nerve by liranches which enter the 

 superficial aspect of the muscle near its outer border about the middle of the leg. 



Action. — To flex the last phalanges of the four outer toes; it will then help to 

 flex the second and first phalanges and the medio-tarsal joint of the foot. It will 

 also help slightly in the extension of the ankle-joint. In flexing the medio-tarsal 

 joint, it will tend to preserve the arch of the instep. 



Relations. — Superficially, in the leg the soleus, posterior tibial vessels and 

 nerve; in the foot, the abductor hallucis and flexor brevis digitorum. Deeply, the 

 tibialis posticus in the leg, and in the foot the tendon of the flexor longus hallucis, 

 the accessorius, and the muscles which form the inner part of the third layer of the 

 sole of the foot. 



Variations. — An accessory head sometimes arises in the leg from the fibula, the tibia, or the 

 deep taseia ut' the leg ; it may join the rest of the muscle iu the leg, or in the sole. Some of the 

 tendons to the toes may be wanting ; more often they are increased in number and supply 

 the deficiencies of the flexor brevis digitorum, and especially by sending slips to the little toe. 



2. FLEXOR LONGUS HALLUCIS 



The flexor longus hallucis — named from its action ujion the great toe (hallux) 

 and its length — is a strong fusiform sheet. 



Origin. — The lower two-thirds of the posterior (or flexor) surface of the 

 fibula external to the oblicjue line; (2) the intermuscular septa between it and the 

 tibialis posticus in front, and the peronei outside; (3) the deep fascia covering its 

 jiosti'rior surface; and sometimes (4) the lowest portion of the interosseous mem- 

 l)rane. 



Insertion. — (1) Tlie under surface of the base of the last jdialanx of the great 

 toe; (2) by a small slip into that part of the flexor longus digitorum tendon which 

 is distributed to the second and third toes. 



Structure. — The nmscle arises by fleshy fibres which ]iass with a l)i})enniform 

 arrangement into the tendon. This tendon appears first just below tlie middh:" of 

 the leg at the back of tlie muscle near its inner border. The fleshy fibres are 

 inserted into it as far as the ankle-joint, and just above this point the tendon passes 

 through the groove at the outer ])art of the back of the lower end of the tibia. The 

 tendon then grooves tlie l)ack of the astragalus, and afterwards the under sin-face of 



