384 



ANIMAL MECHANICS. 



and to its inner side. When the thigh is abducted, these 

 muscles form plane quadrilaterals, and I have already shown 

 (p. 328) that they are nearly inscribable in circles, which is 

 the geometrical condition necessary to produce the maximum 

 work. 



In Fig. 98 I have drawn these muscles to scale, from the 

 measurements given in p. 328. The pelvic origin is AB, 

 and the femoral insertion is AB' . If the quadrilateral 

 ABB 1 A' be inscribable in a circle, then \iA'A and B'B be 

 produced to meet in 0, and OYX be drawn bisecting the 

 angle A OB, the triangle CXY should be isosceles, and the 

 side CX equal to the side CY. I found the following mea- 

 surements, on the scale of nature : — 



CX = 4 29 in 

 CF= 4 -3o „ 



From this result we can calculate the ratio which the work 

 actually done by the muscle bears to the maximum work pos- 



Y 



Fig. 99. 



sible. Let CXY (Fig. 99) be the same triangle as in Fig. 98, 

 and let SC be the axis of rotation passing through the 

 socket 8. Draw through XYihe plane YPX perpendicular 



