ANIMAL MECHANICS. 



135 



The following considerations will serve to show more 

 clearly, the important mechanical differences involved in the 

 Tables of cross sections of the flexors of the hand and foot. 



The mechanism of a true hand, or grasping organ, may be 

 thus illustrated. 



Let OA, AB, and BC, represent three bars turning upon 

 hinges at A and J5, and acted upon by a muscle Om, attached 



Fig. r 9 . 



to a tendon mxy, this tendon being inserted at y, and pass- 

 ing through a loop or pulley at x. When the muscle Om 

 contracts, the system of bars will take the position OA'B'C, 

 which is more flexed than the position OABC, or in other 

 words, the angles at A' and B' are smaller than the angles at 

 A and B. In this movement of flexure, the muscle Om is 

 shortened, while the tendon mxy remains equal in length to 

 the tendon m'x'y' ; but since the angle at B' is smaller than 

 the angle at I?, the base of the triangle, yx', is shorter than the 

 base yx, and therefore the tendon is drawn through the loop 

 x in the direction of the arrow, towards the point 0 ; hence 

 the friction of the loop x f , which is opposite to the direction 

 of the motion, assists the part of the tendon yx, which is 

 situated below the loop. If therefore the force of the muscle 

 be denoted by F, and the friction of the loop by F; we shall 



