ANIMAL MECHANICS. 



33 



Work done by Shoulder Mus-^| 



cles, holding the loaded I 27 ca. 8 n „ 



a 1 • n V = — — = 2.2 K ft. lbs. 



Arms horizontally, per j 226 x 4.5 ° J 



ounce, per second. J 



Having thus found the work done by the muscles of the 

 shoulder, I proceeded to check the result by observations made 

 on the muscles of other parts of the body ; and after trying 

 many experiments on other muscles, such as the pronators of 

 the forearm, and the openers of the jaw, &c, I finally se- 

 lected as the most reliable the following experiments made 

 on the flexors that hold the forearm in the horizontal position 



If the forearm be held, with the palm of the hand up- 

 wards, in the horizontal position, it is allowed by all authors 

 on Animal Mechanics, that it is kept in that position by the ac- 

 tion of the biceps humeri, and of the brachiceus or brachialis anti- 

 cus; to these muscles must be added the supinator radii lo?igus 9 

 which in the horizontal supine position of the forearm acts as 

 a flexor cubiti, and has a resultant that passes above the axis 

 of the elbow joint. 



On holding a weight suspended from the wrist, with 

 the forearm in the position described, it is found that the 

 feeling of fatigue commences on the outer side of the lower 

 half of the arm, with the supinator, then extends to the biceps 

 humeri, and finally reaches the brachiceus, when the experi- 

 menter is forced to yield to the insupportable feeling of fa- 

 tigue, and to confess that he can hold out no longer. 



In the following experiments, I have made use of the same 

 persons who so kindly aided me in the experiments on the 

 muscles of the shoulder. 



The total work done is expressed, as before, by the 

 equation 



Total work = w (iv + a) xt, (9) 

 D 



