260 



Rev. S. Haughton on the 



[Mar. 10, 



In order to ascertain the force of the muscles, I measured carefully their 

 average thicknesses in three subjects, of whom one was a young woman 

 who had borne children, and the others were men of ordinary size and ap- 

 pearance. The results obtained were the following : — 



Thicknesses of Abdominal Muscles. 





No. 1. Male. 



No. 2. Female. 



No. 3. Male. 





in. 



in. 



in. 





0-275 



029 



0-34 





0-200 



0-25 



0-19 





0-235 



017 



024 





0-127 



015 



014 







Total 



0-837 



0-8G 



091 



The average total thickness of the muscular walls is 0*869 inch, which 

 is nearly identical with the measurement obtained from the female subject. 

 It has been ascertained by careful observations, that we must add 50 per 

 cent, to the weights of muscles in the dead subject in order to bring them 

 to the living weights; this correction gives us 1*3035 inch for the mean 

 thickness of the muscles causing tension in the central line of the belly, 

 where the forces of all the muscles come into play together. Multiplying 

 this thickness by 102'55 lbs., or coefficient of muscular contraction, we 

 find 



T=l-3035xl02'55 = ]33-67 lbs. 

 This is the tensile strain producible by the contraction of the abdominal 

 muscles along the curved central line of the belly. 



It remains now to ascertain the principal curvatures of the abdominal 

 surface, and to use the equation 



^Pi PJ 



so as to determine P, the hydrostatical pressure per square inch inside the 

 cavity of the belly, and available, either in whole or in part, for the expul- 

 sion of the foetus during the second stage of labour. 



In order to ascertain the curvature of the belly, I made experiments on 

 three young men placed lying on their backs upon the floor, and made 

 them depress and raise the abdominal wall as much as possible. The result 

 was as follows : — Taking a straight line from the upper part of the sym- 

 physis pubis to the xiphoid cartilage as the fixed line of comparison, it was 

 found possible to depress the navel one inch below this fixed line and to 

 raise it two inches above it. When the belly was distended to the utmost 

 by the action of the abdominal muscles, I measured the longitudinal and 

 transverse curvatures by measuring the sagittas corresponding to a given 

 length of tangent, with the following results : — 



