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ANIMAL MECHANICS. 



This result is comparable with the expulsive force of the ab- 

 dominal muscles acting at the navel, although inferior to 

 their maximum force exerted near the pubes. 



Muscular Skew Surfaces. 



The last and most complex muscular surfaces to be con- 

 sidered are those corresponding with skew surfaces in 

 geometry. The simplest form of skew muscle occurring in 

 nature is that shown in Fig. 54, where AB and A'B' are two 



Fig- 54 



bones not lying in the same plane, and each divided into an 

 equal number of parts, such that the anharmonic ratio of any 

 four points on one bone is equal to the anharmonic ratio of the 



