492 THE MUSCULATURE 



it overlies skeletal structures it becomes adherent to them. In the main this fascial sheet is 

 thin. Over the base of the first metatarsal it is strengthened by a band which runs from the 

 medial side of this bone over the extensor tendons of the big toe to the base of the second 

 metatarsal. The extensor digitorum brevis is covered by an adherent fascial sheet. The 

 dorsal surface of each dorsal interosseous muscle is likewise covered by an adherent membrane. 



The plantar surface of the foot is invested by a fascia in which three distinct regions may 

 be observed, a central, a lateral, and a medial. The central region is greatly thickened by 

 bands of fibrous tissue, the plantar aponeurosis, which diverge toward the toes from the medial 

 half of the tuber calcanei. These bands become distinct from one another as the toes are 

 approached, and each finally terminates partly in the skin over the head of the corresponding 

 metatarsal and in the digital sheath of the flexor tendons. Some of the fibres are continued 

 into the transverse capitular hgaments, the others extend through near the metatarsophalangeal 

 articulation to the dorsum of the foot. Broader, thicker bands go to the three middle toes 

 than to the big and little toes. At the margins of this central area some fibres radiate into 

 the fascia of the lateral and medial area, some extend laterally into the skin, and some sink 

 into the intermuscular septa described below. Near the toes well-marked transverse bundles 

 of fibres may be seen between the digital bands. The central area of the plantar fascia is not 

 densely adherent to the skin. 



The digital sheaths of the flexor tendons of the toes correspond essentially with those 

 previously described (p. 387) for the fingers. 



The medial plantar fascia is thin and adherent to the skin. It extends between the central 

 plantar and the dorsal fascia over the intrinsic muscles of the big toe. The lateral plantar 

 fascia is thick and well developed near the heel, thin as the little toe is approached. A dense 

 band, the.calcaneo-metatarsal ligament, strengthens it between the calcaneus and the tuberosity 

 of the fifth metatarsal. 



At the junction of the lateral with the central region of the plantar fascia the lateral inter- 

 muscular septum sinks in to be attached to the first cuneiform, the navicular and the tendon 

 of the posterior tibial. A similar medial intermuscular septum sinks in between the medial and 

 central regions of the plantar fascia and is attached to the long plantar ligament, the tendon 

 sheath of the peroneus longus and the base of the fifth metatarsal. The fascia of each of these 

 regions in considerable part extends into these septa instead of becoming continuous across them. 



The sole is thus divided into three great fascial compartments by these septa, a lateral, a 

 central, and a medial. In the lateral lie the intrinsic pedal muscles of the little toe; in the 

 medial, the abductor and the flexor brevis of the big toe and the distal end of the tendon of 

 the flexor hallucis longus. The central compartment is subdivided by transverse septa into 

 several sub-compartments. In the most superficial compartment lies the flexor digitorum 

 brevis; in the second, the tendons of the flexor digitorum longus and its associated nmscles, 

 the quadratus planta; (flexor accessorius) and the lumbrical muscles; in the third, the adductor 

 muscles of the big toe; and in the fourth, the interosseous muscles. 



The first two sub-compartments are most clearly marked in the region of the tarsus. 

 Distally they become merged by the disappearance of the intervening transverse septum, and 

 longitudinally subdivided by fibrous septa which serve to make a complete sheath over each 

 digit for the flexor tendons. The sheath over the adductor muscle of the big toe is a thin mem- 

 brane continued laterally from the medial intermuscular septum. Where the two heads of the 

 adductor muscle advance upon their tendon of insertion, the medial septum has no skeletal at- 

 tachment, so that the adductor sub-compartment of the middle fascial compartment com- 

 municates freely with the medial compartment. Over the cuneiform bones the tendon of 

 the flexor hallucis longus passes from the long flexor region of the middle compartment into 

 the medial compartment. Here the medial intermuscular septum divides into two layers, 

 which form a sheath for the tendon as it passes to the plantar surface of the flexor hallucis 

 brevis. 



MUSCLES 



1. Muscle of the Dorsum of the Foot 



The extensor digitorum brevis (fig. 418). — This muscle is broad and thin, 

 lies beneath the tendons of the long extensor muscle on the tarsus, lateral to the 

 navicular and the head of the talus, and sends tendons to the four more medial 

 toes. It ari.scs from the calcaneus. Its nerve-supply is from the deep peroneal. 



Origin. — From the lateral and superior surfaces of the body of the calcaneus and from the 

 apex of the cruciate hgament. 



Sir uct lire and inserlion. — The fibre-bundles arise directly from the hgament, and by short 

 tendinous bands from the bone. As they extend distally they become grouped into four bellies. 

 Those of the most medial and largest belly, the extensor hallucis brevis, become inserted in a 

 bipenniform manner on the lateral and medial margins of a tendon which begins opposite the 

 cuboid. The insertion of fibre-bundles continues to the base of the first metatarsal. The in- 

 sertion of the fibre-bundles of the other l)cllies, which are seldom so distinctly isolated as the 

 first, takes place in a penniform manner into their respective tendons, but the exact mode of 

 attachment is subject to great individual variations. The tendon of the first digit is inserted 

 mainly into tlie middle of the; back of the base of the first plialanx, but it is often also united 

 to the tendon of the long extensor. The other three tendons are fused with the lateral margins 

 of the corresponding tendons of the long extensor near the bases of the three middle digits. 

 They also usually give shps to the ba.ses of the first phalanges of the corresponding toes. 



