ANIMAL MECHANICS. 



159 



and resistance to be overcome, must be the descendant from 

 ancestors who attained this proportion accidentally, and trans- 

 mitted it to their posterity, who thus acquired an advantage 

 over their neighbours in the competition for life. Thousands 

 and tens of thousands of those who have preceded us must 

 have perished in the race, from not having had the precise 

 balance between uterine force and resistance, which we hap- 

 pily possess ; and we may regard ourselves as the survivors of 

 a contest in which the slain greatly outnumber the victors. 

 According to this School of Philosophy, an economy of two 

 per cent, of wax will make a bee ; and a saving of a quarter 

 ounce of uterine tissue may, possibly, constitute the sole dif- 

 ference between a Celtic and a Teutonic woman. 



Happy is the man whose mother possessed the hereditary 

 tendency to form no more uterine muscle than was absolutely 

 necessary to push him into the world ! Happy is the bee who 

 can form her cell with a saving of two grains of wax in the 

 hundred, for she will distance in the race of life her compe- 

 titors who have not inherited this precious art ! 



In the second stage of labour, the voluntary action of the 

 abdominal muscles is called into play, to aid the expulsive 

 efforts of the uterine muscles. I have attempted to calculate 

 the force available from the contraction of these muscles as 

 follows : — 



The abdominal muscles are four in number, viz. rectus 

 abdominis, obliquus externus, obliquus interims, and transver- 

 salis. The last three muscles form curved sheets, acting 

 upon the corresponding muscles of the opposite side by means 

 of tendinous aponeuroses which meet in the linea alba, and 

 form the sheath of the vertical rectus abdominis muscle. From 

 the arrangement of all four, it is plain that the tensile force of 

 muscular contraction in the curved wall of the belly from the 

 xiphoid cartilage to the symphysis pubis, is to be measured 



