248 



ANIMAL MECHANICS. 



Whenever, therefore, the arm is depressed by the latissimus 

 dorsi, from 27 0 23' to 69 0 23', passing through an arc of 42 0 , 

 a greater angular velocity will be attained, in passing through 

 a given angle, than is possible for any other motion of the 

 arm. Kacket players, cavalry soldiers, and others who 

 require to give a swift back stroke with the arm, instinctively 

 learn the proper range of depression, and the relations of 

 position of the muscle, socket, and arm, are all arranged in 

 strict conformity with Proposition B. 



In the action here described, the muscles which extend 

 the forearm upon the arm act in unison with those which 

 depress the humerus, and it is interesting to compare their 

 relative forces. I determined the weights of the two groups 

 of muscles in a male and female subject, with the following 

 results : — 



Depressors of Arm. 



Male. Female. 

 Latissimus dorsi, . . . . 7.55 oz. 4.58 oz. 

 Teres major, 4-09 oz. 1.67 oz. 



1 1.64 oz. 6.25 oz. 



Extensors of Forearm. 



Male. Female. 



Triceps longus, ~\ 



,, interims, > . . . 13.10 oz. 6.59 oz. 

 ,, externus,) 



Ratio of Depressors of Arm to Exte?isors of For ear 7 



Ml I I 64 



Male, ....... 0.80 



13 10 



Female, -— - o.oc 



659 



Mean, . . 092 



