612 MUSCULAR SYSTEM 
Jumenius and Rhamphastus, or from the ium only as in Larus, 
Ardea, Grus, Corythaiz and Podargus. It is frequently connected 
aponeuroticaily with the im. ischio-fleorius, and when its “accessory ” 
is absent, both are inserted on the tibia by one common tendon. 
M. ischioflecorius or semimembranaceus, ribbon-shaped, running 
parallel to the posterior margin of the preceding, present in all 
Birds, though sometimes much reduced, as in Podicipes, Columbx and 
Pierocles, 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-flecorius, being often connected with it in various 
ways. 
M. iliofibularis 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! 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 Rhamphastide and Cuculidex, the main stem goes to 
the third toe, and sends a short slip to each of the others. In the 
Picidzx 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 Psiétact 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. 
