THE CRURAL MUSCLES. 655 



3. PoPLiTEUS (Fig. 622). 



Attachments. — The popliteus arises by a narrow tendon from the outer con- 

 dyle of the femur and by a sHp from the posterior Hgament of the knee-joint. It 

 passes inward and downward to be inserted into the posterior surface of the tibia 

 above the obHque hne. 



Nerve-Supply. — By the internal popliteal (tibial) division of the greater sciatic 

 nerve from the fifth lumbar and first sacral nerves. 



Action. — To fiex the leg and rotate it inward. 



Relations. — On its posterior surface it is covered by the plantaris and gas- 

 trocnemius, and it is crossed by the popliteal vessels and internal popliteal nerve. 

 By its deep surface it is in relation to the capsule of the knee-joint, a bursa (bursa m. 

 poplitei) intervening. 



Variations. — The most frequent anomaly in connection with the popliteus is the occurrence 

 of a second head, which arises from the sesamoid cartilage of the lateral head of the gastroc- 

 nemius. The occurrence of this head is frequently associated with the absence of the plantaris. 



{b) THE POST-AXIAL MUSCLES. 



1. Tibialis anticiis. 4. Extensor longus hallucis. 



2. Extensor longus digitorum. 5. Peroneus longus. 



3. Peroneus tertius. 6. Peroneus brevis. 



Tibialis Anticus (Fig. 623). 



Attachments. — The anterior tibial muscle (m. tibialis anterior) arises from the 

 outer tuberosity and surface of the tibia and also from the interosseous membrane 

 and the crural fascia. Its fibres extend downward to a strong tendon which passes 

 through the inner compartment of the anterior annular ligament and is inserted 

 into the inner surface of the internal cuneiform and the base of the first me<:atarsal 

 bone. 



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

 and first sacral nerves. 



Action. — To flex the foot ; to draw up the inner border and hence invert the 

 sole. 



Relations. — The anterior tibial rests upon the lateral surface of the tibia and 

 upon the interosseous membrane, and is in contact externally with the extensor 

 longus digitorum, the extensor longus hallucis, and the anterior tibial vessels and 

 nerve (Fig. 617). A bursa (bursa subtendinea m. tibialis anterioris) intervenes 

 between its tendon and the medial cuneiform bone. 



Variations. — Not infrequently a bundle is detached from the muscle to be inserted into the 

 anterior annular ligament, into the dorsal fascia of the foot, or, in some cases, into the astragalus. 

 It forms what has been termed the tibio-fascialis anterior or tibio-astragalus. 



2. Extensor Longus Digitorum (Fig. 623). 



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

 arises from the external condyle of the tibia, the upper part of the fibula, the in- 

 terosseous membrane, the intermuscular septum, and the crural fascia. Its fibres 

 pass downward and terminate at about the middle of the leg in a tendon which passes 

 through the outer compartment of the anterior annular ligament and divides into four 

 tendons which pass to the second, third, fourth, and fifth toes. Over the metatarso- 

 phalangeal joint of its digit each tendon spreads out into a membranous expansion 

 which covers the dorsum of the first phalanx and receives the insertions of the inter- 

 ossei and lumbricales, and, in the case of the second, third, and fourth toes, those of 

 the extensor brevis digitorum. Distally each membranous expansion divides into 

 three slips, of which the middle one is inserted into the second phalanx and the 

 lateral ones into the third phalanx of its digit. 



Nerve-Supply. — From the anterior tibial nerve from the fourth and fifth lum- 

 bar and first sacral nerves. 



 Action. — To extend the second, third, fourth, and fifth toes and to flex the foot. 



