ANIMAL MECHANICS. 



259 



of the line OX ; so that our conclusions, with respect to the 

 biceps, will apply to all the hamstring muscles. 



Let £ be the centre of the acetabulum. 0 the tuber ischii, 

 C the centre of motion of the knee joint, and 1 the top of the 

 fibula I obtained the following measurements from the male 

 Tiger, already mentioned at p. 127 : — 



The distances OS, SC. anc 67 aie absolutely fixed; but the 

 distance 01 may be shortenec by the action of the biceps and 

 other hamstring muscles. 1 have taken the length of 01 at 14 

 inches, before the contraction of the muscles. 



Let us first inquire w 7 hat range of motion the leg can 

 have, before the line 01 is shortened 01 extended. This 

 question gives us the quadrilateral figure OSCl, whose four 

 sides are given; and we are required to move the quadrilateral 

 about OaS regarded as fixea, so as to find the extreme limits 

 possible for its construction. With 0 as centre, describe the 

 circle I'll" ; and with S as centre, describe the circle C'CC' . 



The leg of the Tigei may be moved forward, or flexed 

 upon the body, until the lines 01 and IC form one continued 

 right line, in the position 01" C, where T'C" is equal to 

 1C; the leg cannot be moved forward beyond this position 

 without lengthening the muscle OIX, and thus provoking it 

 to contract. The leg of the Tiger may be moved back- 

 wards, or extended upon the body, until the lines SC and CI 

 form one continued right line, in the position SC'T, where 

 C I' is equal to CI ; and the leg cannot be moved farther 

 backwards without a shortening of the muscle OIX. Pro- 

 duce the line OS to O', and measure the angles O'SC" and 

 O'SF, which represent the extreme limits of the position of 

 the leg, compatible with the supposition, that the muscle 



OS = 5.49 in. 

 SC - n.75 v 



CI = 2. 63 in. 

 07=14.00 „ 



s 2 



