364 Elementary Principles in Animal Mechanics. [Apr. 29, 



It appears to be highly probable that, in all cases, the most useful 

 work will be done when the resistance to be overcome is eqnal to the 

 weight of the limb itself, estimated as applied at the same distance 

 from the centre of motion as the resistance or weight. 



I attempted, in the following manner, to check the value found 

 for a, the equivalent of the arm and shoulder, estimated at the middle 

 of the hand. 



Dr. Macalister, closing his eyes, had his arm suspended to a balance 

 by a string looped round the middle of the hand, and the weight of 

 the suspended arm, allowed to hang " dead," was measured by weights 

 placed in the opposite scale. 



After many trials, I found the weight to be 5 lbs. with a possible 

 error of 2 ozs., or + 0125 either way. 



To find the effect of the shoulder, I measured the horizontal distance 

 of the centre of gravity of his scapula from the centre of his glenoid 

 cavity, and found it to be 3J inches, while the distance of the middle 

 of his hand from the same centre was found to be 22 inches. 



The weights lifted with the scapula were thus estimated : — 



Muscles.* 1 ozs. 



Supraspinatus 1*85 



Infraspinatus 3*51 



Teres major 3*30 



Teres minor 1*19 



Subscapularis 3*88 



Deltoideus (half) 5'90 



Trapezius (one-third) 2*40 



Serratus magnus (two-thirds) 3*92 



25-95 ozs. 



To this must be added about one-third more, to represent fat, fascia, 

 tendons, and skin, or 8*65 ozs., making" altogether 34"60 ozs. 



As these weights were all obtained from dead subjects, we must add 

 somewhat more than one half,f to bring the weights up to the 

 standard of the living subject, which makes altogether over 51 "90 ozs. 



Adding to this the weight of the average fresh scapula, 4*5 ozs., we 

 have, finally for the total weight applied at the centre of gravity of the 

 scapula, 56*40 ozs., which, when reduced to the corresponding weight 



3*5 



held in the palm of the hand, gives 56*4 x — — =8*97 ozs. = 0*56 lb. 



U -I 



Adding this result to the weight of Dr. Macalister's arm, estimated 



* " Principles of Animal Mechanics," p. 406. 

 f " Principles of Animal Mechanics," p. 45. 



