ANIMAL MECHANICS. 



231 



It is interesting to observe that the tension in the vertical 

 direction produced by the external oblique muscle, varies as 

 the distance of the point of the linea alba under consideration 

 from the sternum, which is precisely the law according to 

 which the pressure of the contents of the abdomen, regarded 

 as semi-fluid, would vary ; viz., as the depth of the fluid 

 measured from its surface. 



The Diaphragm, which forms the upper surface of the 

 abdominal cavity, furnishes an example of a convex ellip- 

 soidal muscle ; it is used continually in respiration, and 

 occasionally in the expulsion of the contents of the abdomen. 

 Its force is considerable, although not equal to the maximum 

 effort of the abdominal muscles ; and being an involuntary 

 muscle not under our control, when it provokes the abdominal 

 muscles to take on a violent reflex action, as in coughing, its 

 effects are sometimes dangerous, as, for example, in cases of 

 hernia. It is, therefore, important, not merely in a scientific 

 but also in a practical point of view, to know the amount of 

 hydrostatical pressure it is capable of producing upon the 

 contents of the abdomen. 



From measurements made by me, I infer that the mean 

 curvatures of the diaphragm, when most convex, correspond 

 with circles of 5.601 inches, and 5.109 inches in diameter 

 at the two sides of the body, and that the mean thickness of . 

 its muscular walls is 0.18 in. Adding 50 per cent, to the 

 latter measurement as before, and taking the mean diameter 

 of curvature, we obtain from equation (36) 



p = ^ = iZ 7 ; 



and from the coefficient of muscular force (p. 69), 

 K= 102.55 lbs. 



„ 4 X 0.27 X I02.55 sr, 11 



* = ~~ ~ m = 20.08 lbs. per sq. in. 



