86 ANIMAL MECHANICS 



in the forelegs is strength of the extensor ten- 

 don s, so that the feet may be well thrown out 

 before, for if these tendons be not strong, the 

 joints will be unable to sustain the weight of his 

 body, when powerfully thrown forward, by the 

 exertion of his hind-quarters, and he will be apt 

 to come with his nose to the ground. 



The whole apparatus of bones and joints being 

 thus originally constituted by nature in accurate 

 relation to the muscular powers, we have next to 

 observe, that this apparatus is preserved perfect 

 by exercise. The tendons, the sheaths in which 

 they run, the cross ligaments by which they are 

 restrained, and the bursce mtiscosce 1 which are 

 interposed to diminish friction, can be seen in 

 perfection only when the animal machinery has 

 been kept in full activity. In inflammation, and 

 pain, and necessary restraint, they become weak ; 

 and even confinement, and want of exercise, with- 

 out disease, will produce imperfections. Exercise 

 unfolds the muscular system, producing a full 

 bold outline of the limbs, at the same time that 

 the joints are knit, small, and clean. In the 

 loins, thighs, and legs of a dancer we see the 

 muscular system fully developed ; and when we 



1 These bursce mucoscz (mucous purses) are sacs containing a 

 lubricating fluid. They are interposed wherever there is much 

 pressure or friction, and answer all the purposes of friction- wheels 

 in machinery. 



