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ANIMAL MECHANICS. 



the preceding calculations, that the uterus can never destroy 

 itself by its own contraction. It would, indeed be, a priori, 

 ridiculous to suppose that Nature would produce an involun- 

 tary muscle capable of destroying itself, and so causing the 

 death of its owner, by its own blind force. 



In concluding my remarks on the uterine muscles, I may 

 observe that the arrangement of these muscles on various 

 parts of the organ affords a confirmation of the accuracy of 

 Lagrange's principle as applied to them. It is well known 

 that these muscles attain their greatest thickness at the fundus 

 of the womb, where they are fully double the thickness of the 

 muscular layer at the neck of the womb. Now, so long as 

 the contents of the womb are fluid, or semi-fluid, a constant 

 pressure is exerted perpendicularly to all portions of its walls, 

 requiring by Lagrange's theorem (20), a tensile muscular 

 force varying as the diameter of curvature at each point. 

 From observations on the curvature of the gravid uterus, it 

 may be inferred that the diameters of curvature at the fundus 

 and neck of the womb are nearly in the proportion of 29 

 to 17. When the womb is emptied of its contents, and the 

 uniform hydrostatical pressure inside is removed, the uterine 

 walls contract with degrees of force proportional to the dia- 

 meters of curvature they possessed in their former condition ; 

 the fundus contracting with twice the force of the parts near 

 the neck — an action eminently calculated to promote the safe 

 and speedy reduction of the organ to its diminished bulk, 

 without risk of inversion. 



It is worth while to consider, for a moment, the explana- 

 tion offered by the Lamarckian Theory of Natural Selection, 

 of the relation between the strength of the uterine muscles 

 and the resistance of the membranes they are required to 

 rupture. According to this theory, an animal that possessed 

 such a proportion as I have shown to exist between the force 



