Hitman Physiology. 



169 



the hinder part of the eye-ball. There are dozens of adaptations 

 in the eye itself far more wonderful than this ; but we are struck 

 with the simplicity of a contrivance so like what we should make 

 ourselves. 



The elbow-joint, as any one may observe, is a 

 perfectly stiff hinge-joint, yet the hand can be 

 turned more than half-way round. It is managed 

 in this way. One of the two bones of the arm is 

 fixed in the elbow-joint, the other equally fixed at 

 the wrist but each has a free end which revolves 

 in a band on the other. Fig. 23 shows the two 

 muscles by which the hand, which naturally lies on 

 its back, can be turned over so as to -lie on its 

 palm. 



It was necessary to the elegance and beauty 

 of the body that the ankles and wrists should be 

 small, and neither feet nor hands loaded with 

 muscles ; yet fingers and toes must have many 

 powerful muscles to accomplish all their motions 

 muscles for every joint of every finger. To accom- op THE 

 plish this, the muscles are placed in the arm and 

 leg, and they are connected with the bones they are to move 

 by slender white cords, playing in sheaths, called tendons. 

 These tendons at the ankle and wrist would pull up the skin, 

 .and spoil the shape of the limb, but that has been prevented 

 by confining them with a strong tight band, as seen in Fig. 24. 

 They also divide on the knuckles to avoid being pulled down 

 -on either side. 



On the inside of the hand is a still more curious arrange- 

 ment. The tendons of the muscles, which move the second 

 joint of the fingers, divide to let the tendons of the flexors of. 

 the first joint pass through them, as shown in Fig. 25, where 

 also may be seen the curious arterial arch, which gives off 

 arteries for the four fingers. 



Fig. 23. 



