160 



ANIMAL MECHANICS. 



by the sum of the united forces of all the muscular sheets. If 

 we knew the force of each muscle, and the principal curva- 

 tures of the belly in the middle line, we could calculate, by 

 Lagrange's theorem, the hydrostatical pressure inside the ab- 

 dominal cavity, and available to expel faeces, urine, or a 

 foetus. 



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 appearance. The re- 

 sults obtained were the following : — 



Table XXVI. — Thickness of Abdominal Muscles. 





No. 1.— Male. 



No. 2.— Female. 



No. 3.— Male. 



Rectus abdominis, . . 



o. 275 in. 



0 29 in. 



0. 34 in. 



Obliquus extemus, . 



O. 2CO „ 



0. 25 



0.19 „ 



Obliquus inter nus, . 



0.235 »> 



0.17 » 



0. 24 ,, 



Transversalis, 



O. I 27 ,, 



0. 15 ,1 



0. 14 „ 



Totals, . . 



0. 837 in. 



0. 86 in. 



0.91 in. 



The average total thickness of the muscular walls is 0.869 

 inch, which is nearly identical with the measurements ob- 

 tained from the female subject. It has been already explained 

 (p. 46), that we must add 50 per cent, to the weight of mus- 

 cles in the dead subject, in order to bring them to the living 

 weights. This correction gives us 1.3053 inches, 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 coeffi- 

 cient of muscular contraction, we find, 



T= 1.3035 x 102.55 = !33- 6 7 lbs - 

 This is the tensile strain producible by the contraction of the 



