612 MUSCULAR SYSTEM 



Numenius and fihamphastus, or from the ilium only as in Larus, 

 Ardea, Grus, Corythaix and Podargus. It is frequently connected 

 aponeuroticaily with the m. ischio-flexorius, and when its " accessory " 

 is absent, both are inserted on the tibia by one common tendon. 



M. ischio-flexorius or semimembranaceus, ribbon-shaped, running 

 parallel to the posterior margin of the preceding, present in all 

 Birds, though sometimes much reduced, as in Podicipes, Columbze and 

 Pterodes, arising chiefly from the outer face of the middle or distal 

 third of the ischium and inserted by a flat tendon on the neck of 

 the tibia, whether on its anterior crest or the posterior or inner 

 face. A slip from the principal tendon frequently descends the leg 

 and is inserted either separately or jointly with a similar tendon of 

 the m. caud-ilio-flexorius, being often connected with it in various 

 ways. 



M. ilio-fibularis or biceps cruris, arising from a great portion of 

 the lateral and dorsal margin of the post-acetabular ilium, changing 

 near the knee to a round and strong tendon that, accompanied by 

 one of the principal stems of the ischiadic nerve, runs over a ten- 

 dinous pulley x and passing between the outer and middle head of 

 the m. gastrocnemius is inserted on the tuberosity of the fibula at 

 about the level of the first fifth of the tibia. 



M. extensor digitorum communis, arising from the outer and 

 anterior face of the crest and proximal half of the tibia, its 

 roundish tendon passes mesially from that of the m. tibialis anticus 

 through the transverse ligament along the anterior metatarsal groove 

 and, arrived at its distal end, splits into several tendons, according 

 to the number of front toes, to be inserted on the dorsal surface of 

 the base of their several phalanges. In Striges and Pandion, where 

 the fourth toe is reversible, the principal tendon first splits into two, 

 one for the second toe, the other soon subdividing for the third and 

 fourth. In the Rhampliastidaz and Cuculidx, the main stem goes to 

 the third toe, and sends a short slip to each of the others. In the 

 Picidse the tendon for the fourth toe passes through an ossified loop 

 and over a furrow at the end of the fourth metatarsal, so as to 

 ensure the extension of this digit with the others notwithstanding 

 its backward position. In the Psittaci alone the principal tendon 

 sends a slip to the hallux also, the rest being divided into an inner 

 and outer half, each of which splits again to be inserted on the 

 other toes, the third of which therefore receives two such tendons. 



M. extensor hallucis, arising from the anterior and inner face 

 of the proximal part of the second tarso-metatarsal and inserted 



1 This pulley or loop on the outer side of the knee is composed of three arms, 

 two arising from the outer face of the external femoral condyle, the third from 

 the inner head of the m. perforat. dig. iv. and supporting the outer of two 

 principal branches. Owing to the pulley the contraction of this muscle does not 

 merely draw the leg towards the trunk, but also lifts it towards the thigh. 



