ANIMAL MECHANICS. 



OIX has been neither lengthened nor shortened. We find — 



OSC" = 31 0 

 O'SC = 10 5 0 



showing a range of 74 0 of motion round the socket through 

 which the biceps and other hamstrings are neither lengthened 

 nor shortened. 



When the leg attains the position CT, the angle SOI' is 

 83 0 , and shortly afterwards passes through 90°, when the ham- 

 string muscles contract. If we examine the angle CIO, at 

 the point when the angle 801' is approaching a right 

 angle, and when the hamstring muscles are producing their 

 maximum effect with respect to the hip joint S, we shall see 

 that CI O becomes acute, and that it is far removed from the 

 position in which its maximum effect would be produced 

 upon the knee joint C. In fact, the position of the leg, in 

 which the hamstring muscles would produce their maximum 

 effect upon the knee joint, corresponds with the point c, from 

 which a tangent ci, to the circle would be equal to CI. 



In this position of the leg, the angle ciO is 90 0 , while the 

 angle SOi, corresponding to it, is only 64 0 . From this it fol- 

 lows, that the knee joint is not related to the hip joint, in the 

 same way that the elbow joint is related to the shoulder joint ; 

 and that it is not intended that the muscles acting upon each 

 should attain their positions of maximum effect at the same 

 time. 



In the Tiger's leg, it is the ankle joint that bears to the hip 

 joint, the same relation that the elbow bears the shoulder 

 joint, in the arm ; for, let Ybe the centre of the ankle joint, 

 and join YB to the calcaneum ; and let G denote the origin 

 of the external gastrocnemius muscle, which acts from G to B. 

 This powerful muscle, and the corresponding internal gastro- 

 cnemius, will produce their maximum effect upon the ankle 

 joint, when the angle YBG becomes a right angle, in con- 



