254 



ANIMAL MECHANICS. 



The point of insertion, Q, of the latissimus clorsi and teres major 

 describes a circle, of which S is the centre, and the fibres of 

 these muscles must be contrived of such a length, that XQ 

 and MQ shall be equal to their respective lengths, when half 

 contracted ; and, supposing the whole contraction to be one- 

 eighth of the length, the lengths of the muscles, before and 

 after contraction, must be — 



Before contraction. After contraction. 



Latissimus dor si, . . . — x QX ^ x QI 

 io 16 



Teres major, . . . . x QM ^| x QM 

 J 16 io 



This corresponds to a range of rotation round S, amount- 

 ing to 2i°, at each side of the line JSC, which is the line of 

 maximum effect. 



While the latissim is dorsi is engaged in shortening itself 

 by one-sixteenth, rotating the arm through 2 1°, into the position 

 SC, the triceps longus also shortens itself by one-sixteenth, 

 and causes the forearm to rotate round C, through an angle 

 of 9 0 30', into the position of maximum effect, in which 01 

 and CI are at right angles ; and in the entire complex down- 

 ward and backward stroke of the Tiger's paw, the arm passes 

 through 42 0 , while the forearm passes through 19 0 . 



It is important to observe that the condition fulfilled by 

 the Tiger's arm, by which the angles SQX, SOI, and CIO 

 become right angles at the same time, and so allow all the 

 muscles of the shoulder and elbow to co-operate together, 

 each acting to the greatest advantage, is not a random con- 

 dition attained by chance ; but must have been the result of 

 deliberate forethought and contrivance. This can be proved 

 by showing that the condition involves rigorous geometrical 

 consequences, which might or might not have been fulfilled 



