162 



ANIMAL MECHANICS. 



The curvature of the distended belly, at the navel, is found 

 to be, from the foregoing measurements, 



i i i i i 



pi pa n-3 6 35 6.3166 4.0596' 



Multiplying this curvature into the tension of the abdomi- 

 nal muscles at the navel, already found, viz. 133.67 lbs. per 

 inch, we obtain, finally, 



1 00.67 



P = — — = 32.926 lbs. per sq. inch. 



This amount of expulsive force, per square inch, is avail- 

 able, although not usually employed to assist the uterus in 

 completing the second stage of labour. If we suppose it ap- 

 plied to a surface of a circle 4^ inches in diameter, the usual 

 width of the pelvic canal, we find that it is equivalent to 

 523.65 lbs. pressure. 



Adding together the combined forces of the voluntary and 

 involuntary muscles, we find, 



Involuntary muscles = 54.106 lbs. 

 Voluntary muscles, =523.65 



Total, . . . 577-75 lbs. av. 



Thus, we see that, on an emergency, somewhat more than 

 a quarter of a ton pressure can be brought to bear upon a re- 

 fractory child that refuses to come into the world in the usual 

 manner.* 



In order to determine, by actual experiment, the expulsive 



* The preceding result will, no doubt, remind the curious and well-informed 

 reader, of the statement made by Mr. Shandy, on the authority of Lithopcedus 

 Senonensis de partu difficili, that the force of the woman's efforts, in strong labour 

 pains, is equal, upon an average, to the weight of 470 lbs, avoirdupois, acting 

 neroendicularly upon the vertex of the head of the child. 



