480 THE MUSCULATURE 



muscles. The proximal arm passes over the tendon of the extensor hallucis longus and then 

 divides into two laj^ers, between which the tendon of the tibialis anterior passes. The deeper 

 ligament mentioned above arises from deep within the tarsal sinus, some of its fibres even 

 from the sustentaculum tali. It then passes forward and medially beneath the long extensor 

 tendons, and divides into two parts, one of which curves about the medial margin of the ten- 

 don of the extensor digitorum longus, the other about the extensor hallucis longus tendon to 

 the under surface of the proximal arm of the V-shaped band. 



The peroneal retinacula are strengthened regions in the fascia which serve to hold the 

 tendons of the peroneal muscles in place. The superior extends from the lateral malleolus into 

 the fascia on the back of the leg, and to the lateral surface of the calcaneus. The inferior 

 overlies the tendons on the lateral surface of the calcaneus, and is attached to this bone on 

 each side of them. Between the tendons it sends a septum to the bone. It is connected with 

 the superficial laj'er of the cruciate ligament. 



The laciniate ligament (internal annular) (fig. 416) is found on the medial side of the ankle. 

 Here the fascia is strengthened by fibre-bands which form a well-marked ligament that holds 

 in place the tendons of the deep dorsal cruro-pedal muscles. This ligament extends from the 

 dorsal and distal margins of the medial malleolus to the calcaneus. It is closely bound to the 

 tibia and the talo-tibial (tibio-astragaloid) ligament until the tendon of the tibialis posterior is 

 reached. It passes over this and becomes bound to the bony structures on the posterior 

 margin of the tendon. From this attachment two layers, a deep and a superficial, extend 

 backward. The superficial layer extends to the tuber calcanei, and is connected superiorly 

 with the crural fascia. The deep layer, which represents a continuation distally of the trans- 

 verse septum, extends over the tendons of tlie flexor digitorum longus and flexor haUucis longus 

 to the medial surface of the calcaneus, and is closely united to the underlying bone on each 

 side of these tendons, thus giving rise to osteo-fibrous canals. 



MUSCLES 



1. Muscles of thf Feont of the Leg 



(Figs. 415, 418) 



The anterior musculature of the leg consists of four muscles, the tibialis 

 anterior, extensor digitorum longus, peroneus tertius, and extensor hallucis 

 longus. The tibialis anterior has a quadrangular prismatic belly which arises 

 from the lateral side of the tibia and adjacent interosseous membrane in the 

 proximal half of the leg. The tendon passes over the front of the tibia to the 

 first metatarsal. The extensor digitorum longus is a transversely flattened, 

 fusiform muscle, which arises from the superior extremity of the tibia, the anterior 

 crest of the fibula, and the adjacent interosseous membrane, and gives rise to a 

 tendon which passes over the front of the distal extremity of the tibia and sends 

 tendons to the two terminal phalanges of the four more lateral toes. The 

 peroneus tertius represents a more or less completely differentiated portion of 

 the preceding muscle. Its tendon passes laterally through the same osteo- 

 fibrous canal in the same synovial sheath and terminates on the fifth metatarsal. 

 The extensor hallucis longus is a narrow muscle which arises from the distal half 

 of the medial surface of the fibula and the interosseous membrane. Its tendon 

 extends over the ankle to the great toe. The tendons of these muscles are held 

 in place by the transverse and cruciate ligaments described above. 



All the muscles of this group flex the foot. The extensors extend the toes; the 

 peroneus tertius and the extensor digitorum longus evert the foot. The nerve 

 supply is from the deep peroneal (anterior tibial) nerve. 



The tibialis anterior is represented in the arm probably by the brac^hio-radialis and the two 

 radial extensors; the extensor digitorum longus by the extensor digitorum communis and 

 extensor digiti quinti proprius; and the extensor hallucis longus by the extensor pollicis longus. 

 Two abnormal muscles not infrequently found, the abcUictor hallucis longus and extensor primi 

 intornodii liallufis, represent probably the corresponding normal nuiscles of the hand. 



The tibialis anterior (fig. 415). — Origin. — From tlie distal surface of the lateral condyle 

 of the tibia, and the lateral surface of the proximal half of the shaft of the tibia, the adjacent 

 interosseous membrane, the overlying fascia near tlie condyle (tuberosity) of the tibia, and the 

 intermuscuhir sei)tum between it and tlie extensor digitorum longus. 



Slruclnre. — Bipenniform. The fibre-bundles converge upon a flat tendon which begins 

 high in the muscle and emerges on the aiiterior margin of the muscle about the middle of the leg. 

 On the deep surface the implantation of fibre-bundles continues to the transverse crural (anterior 

 annular) ligament. 



hiserlion. — The tendon passes over the front of the tibia to tlie medial side of the foot, 

 where it is inserted into the medial surface of the first cuneiform and the base of the first 

 metatarsal. 



Nerve-supply. — As a rule, a branch from the common peroneal (external popliteal) nerve 

 enters the proximal portion of the muscle by several twigs, and another from the deep peroneal 

 (anterior tibial) enters near the middle of the belly on the lateral edge. 



