on the-Mutioii of the Arm. 413 



which nfFords it most of the leverage it requires. Thus it is 

 not the uppermost portion, a, of the elevating division, (see 

 the Italic letters in figs. 2 and 4,) which is attached to the 

 lowest point, D, of the insertion, because there are succeed- 

 ing fibres (as b, figs. 2 and 4,) which form a less acute angle 

 with the humerus while depressed: whereas it is the lowermost 

 fasciculus (C, fig. 2,) of the lower division, that seeks the 

 highest point, B, of the insertion, because this portion forms 

 the least acute angle with the humerus when elevated (see 

 fig. 3). This trait adds another to the innumerable proofs of 

 the viinute accuracy of the animal organization. 



Any action which requires from either portion, a species of 

 motion contrary to that which it is adapted to produce, — as 

 raising the body by the hands, which requires force from the 

 fibres of velocity, — soon fatigues the muscle. Turning a winch, 

 which is another instance of the same kind, is notoriously a 

 very disadvantageous application of human strength; and any 

 employment in which steady and forcible pushing has to be 

 performed by the arms raised above the head, is extremely 

 fatiguing. In throwing a heavy quoit, which requires both 

 accuracy and force, the arm is swung by the side ; but in 

 throwing a light ball, for which velocity is requisite, the arm 

 is always swung above the head. Cricketers are practically 

 such good physiologists in this respect, that they have enacted 

 a law which compels the bowler to swing his arm by his side 

 in throwing the ball, — because, if the ball were fiung "over- 

 handed" at the wicket, from so near a point as the bowler's 

 station, its velocity would be unmanageable; whereas the 

 " long-throw" who has to send up the ball from a distance, 

 always swings his arm above his head. 



The muscles associated with each division of the pectoralis 

 major bear out the proposed explanation by the analogy of 

 their insertions. Thus the coraco-brachialis, and the anterior 

 fibres of the deltoid, which cooperate with the upper division 

 of the pectoralis major, are attached to the front of the hu- 

 merus, half-way down ; evidently for the purpose of gaining 

 force, which they do want, at the sacrifice of velocity, which 

 they do not. 



On the contrar}', the teres major and latissimus dorsi, which 

 assist the lower division of the pectoralis major in depressing 

 the humerus, act, like that muscle, near the fulcrum of the 

 lever ; being attached to the inner margin of the bicipital 

 groove, just opposite to the pectoralis tendon. These two 

 muscles, indeed, are in several lespects analogous to the two 

 divisions of the pectoralis major. The teres major, which is 

 superior and smaller, and arises from the scai)ula, may be 



