A Bird's Foot 193 



but are held by the mechanical action of certain muscles 

 and tendons in the leg and foot. Of course, the bird 

 can also control these muscles by an act of its will, but a 

 large part of their action is automatic. In some species 

 there is a muscle called the ambiens, which has its rise 

 in the pelvis, passes along the inner side of the thigh, 

 whence its tendon runs over the apex of the angle of the 

 knee joint, and down the leg till it joins the muscles that 

 flex the 'toes. Now when the bird's leg is bent at the 

 joints, as is the case in perching, the tendons of this 

 muscle are stretched over the knee and ankle joints, thus 

 pulling the digits together, and causing them of their 

 own accord to grasp the perch more or less tightly. When 

 a bird wishes to unloose its hold, it simply rises on its feet 

 and relaxes the tendons. 



All birds by no means possess this particular muscle, 

 but all the perchers have some muscular arrangement in 

 the legs and toes that practically answers the same pur- 

 pose. If you will bend your wrist backward as far as 

 you can, you will observe that your fingers will have a 

 tendency to curve slightly forward. This is caused by 

 the stretching of the tendons over the convex part of your 

 bent wrist joints. 



The typical bird has four digits, three in front and one 

 reaching backward. The hind toe is called the hallux, 

 and corresponds to the thumb of the human hand, so 

 that in grasping an object it can be made to meet any 

 of the other toes. But many birds are not provided with 

 a quartet of digits. The ostrich has only two, the inner 



