THE LOWER LIMB 549 



foot, where they terminate in the dorsal venous arch. The super- 

 ficial veins of the sole are all furnished with valves, which are so 

 placed as to direct the flow of blood to the dorsum of the foot. 



Muscles. — ^The muscles of the sole are divided into four layers — 

 first, second, third, and fourth. 



First Layer. — The first layer consists of the following three 

 muscles, named in order from within outwards : abductor hallucis, 

 flexor brevis digitorum, and abductor minimi digiti. All three lie 

 immediately beneath the corresponding divisions of the plantar 

 fascia, each muscle having a compartment to itself. 



Abductor Hallucis — Origin. — The outer head arises from 

 (i) the internal aspect of the inner tubercle on the plantar surface 

 of the tuber calcis ; (2) the deep surface of the internal division 

 of the plantar fascia ; and (3) the internal intermuscular septum, 

 which separates it from the flexor brevis digitorimi. The inner 

 head arises from (i) the lower border of the internal annular 

 ligament on its deep aspect ; and (2) the fibrous structures along 

 the adjacent part of the inner side of the sole, such as the tendon 

 of the tibialis posticus and some of its expansions. 



Insertion. — ^The tubercular enlargement on the inner side of the 

 base of the first phalanx of the great toe. 



Nerve-supply. — ^The internal plantar nerve. 



Action. — (i) To abduct the great toe from the imaginary middle 

 line of the foot, which passes through the centre of the second toe ; 

 and (2) to flex the metatarso-phalangeal joint of the great toe. 

 The tendon of the muscle receives on its outer and deep aspect the 

 fleshy inner head of the flexor brevis hallucis. 



Flexor Brevis Digitorum (flexor perforatus) — Origin. — (i) The 

 front of the inner tubercle on the plantar surface of the tuber 

 calcis ; (2) the deep surface of the central division of the plantar 

 fascia ; and (3) the intermuscular septum on either side. 



Insertion. — By means of four tendons which go to the four outer 

 toes, where each is inserted into the sides of the shaft of the second 

 phalanx at its centre and on its plantar aspect. 



Nerve-supply. — ^The internal plantar nerve. 



Action. — (i) To flex the second phalanges of the four outer toes, 

 and (2) to flex the metatarso-phalangeal joints. 



Each tendon, as it passes along the plantar surface of a toe, has 

 a tendon of the flexor longus digitorum above it as far as the 

 second phalanx, the two tendons occupying a fibro-osseous canal 

 lined by a synovial membrane which furnishes a separate invest- 

 ment for each tendon. Opposite the first phalanx the brevis tendon 

 divides into two parts, and the longus tendon passes through the 

 cleft thus formed; hence the name flexor perforatus for the brevis 

 muscle. Thereafter the two divisions of the brevis tendon unite 

 by their adjacent margins on the upper or d6ep surface of the 

 longus tendon, but they soon separate and take insertion into the 

 sides of the shaft of the second phalanx at its centre and on its 

 plantar aspect. Each brevis tendon has a ligamentum breve 



