ANIMAL MECHANICS. 



257 



the contraction of the muscle always swings the wing through 

 the position corresponding with 0 = SOX =90°, so as to pro- 

 duce, in striking the air, a given angular velocity, with a 

 minimum angle of rotation of the wing. Assuming, as before, 

 the contraction of the muscular fibres to be one-eighth of 

 their length, we readily obtain the following result : — Since 

 OX is equal to 4.62 inches— 



™ 462 , 



SO = -j-—. = — — — = 73 1 



It sin (j) 16 x 220 



Hence the wing of the Albatross, ^when acted upon by the 

 latissimns dorsi, will sweep through an angle of 15 0 , making 

 the angle SOX a right angle in the course of the rotation, 

 and producing a maximum velocity of stroke, for a given 

 angle of rotation. 



(d). Hamstring Muscles of Tiger and Lion. 



The next example of Proposition B that I shall give is 

 taken from the hamstring muscles of the great Felidae, which 

 constitute one of the most wonderful instances of well-devised 

 mechanism to be found in the entire range of the Animal 

 Kingdom. 



In Fig. 68 are shown the pelvis and leg of the Bengal Tiger, 

 in which 0 is the tuber ischii and origin of the biceps femoris 

 muscle, whose extreme fibres are OA, to the middle of femoral 

 fascia, and OB wound round the tendo A chillis, a nd directed 

 towards the calcaneum. The angle A OB is 50 0 , and the 

 bisector OX passes through the top of the fibula, and is the 

 direction of the resultant force of all the fibres of the biceps 

 This great muscle, instead of being inserted into a single point, 

 is spread out, so as to act upon several joints at the same 

 time ; its upper fibres act on the hip joint only ; its middle 

 fibres act upon both the hip and knee joints, and its lower 

 s 



