爬行动物和低等鸟类腿部的一块肌肉.起自髋臼前缘耻骨、髂骨的会合处，与股骨平行的内侧，以一薄腱斜跨膝关节前方，转向外侧经腓骨头外侧至髌骨远端，与第2、3趾屈肌起点的腱相连，止于第2、3趾的远端腹面.当鸟栖息于树枝时，4趾拳曲握枝，后肢几个关节因肌肉收缩而成最小的弯曲角度，体重整个压到后肢，栖肌因而收紧，屈肌亦随之拉紧.即使鸟睡熟了，也会因体重下坠，机械地拉紧栖肌，4趾紧紧地握住树枝，不会跌落下来.当准备起飞时，伸肌收缩，脚趾放松，栖肌松弛，后肢几个长骨形成的杠杆同时向上伸开，使鸟弹跳起来，展开双翅起飞。

Birds, reptiles and lower leg muscle. Starting from the leading edge of the pubic bone acetabulum, ilium of Meeting Point, and the femur parallel to the inside to a thin tendon knee diagonal front, turned to the outside through the fibula head lateral to the patella remote, with the first starting point of 2,3 toe flexor tendon connected to the toe of the distal end with the first 2,3-ventral. When the bird habitat in the branches, the four toes curl grip branches, limbs a few muscle contraction joints formed by the smallest bending angle, weight as a whole down to the hind legs, habitat and thus tighten the muscles, has also undergone flexor strain. Even if the bird fast asleep, and will fall due to body weight, mechanical and taut muscles habitat, 4 toes clasped the branches will not fall down. When you are ready to take off, the extensor contraction, toes relax, habitat muscle relaxation, hind the formation of several long bones at the same time the lever upward stretch, so that birds bounce up and started double - wings to take off.