86 



ANIMAL MECHANISM. 



bones had worn the surfaces smooth ; the humerus continually 

 changing its position, and turning upon its axis, seems to 

 imitate the action we employ when we wish to obtain by 

 means of friction a body of a spherical form. 



It is thus, for instance, that opticians produce the forms 

 and the polished surfaces of convex and concave lenses. At 

 its lower end the shoulder-bone shows the trace of the same 

 phenomenon, a small spherical projection articulating it with 

 the radius ; it shows also that there existed movements of 

 two kinds, and close by, we meet with a surface cut like 

 the groove of a pulley ; this, in fact, only contributed to the 

 flexion and extension of the fore-arm. 



If w^e examine the skull we meet with fresh surprises; here 

 every want is foreseen. Deep cavities lodge in their interior 

 the brain and the organs of sense. 



The nerves have conduits which allow them to pass through ; 

 each vessel creeps along a furrow which forms a canal for it, 

 and is ramified with the minute arteries whose rich foliation it 

 delicately traces out. 



If the bone were not so hard, one would really suppose that 

 it had been subjected to external force, of which it bears, as it 

 were, the imjjression. But it is in vain to press a bony sur- 

 face ; it resists absolutely the force which is applied to it. It 

 is necessary to use a saw or a gouge if we wish to make a 

 channel in it. How could the pressure of soft parts hollow 

 out these cavities which are sometimes so deep ? 



The foresight of nature has prepared everything in the 

 skeleton so that it may be disposed in the best possible manner 

 to receive the organs to which it offers its solid and invari- 

 able support. Such is the natural argument of all those 

 who have not seen, with their own eyes, these osseous changes 

 take place, and these channels hollowed out. The anatomist 

 as well as the zoologist have necessarily reasoned in this 

 manner. They have considered the skeleton as the unalterable 

 element of the organism, and therefore they have derived from 

 it the greater part of the specific characters in zoology. 



It must be very difiicult to oppose an opinion which has 

 been for a long time received. Thus, when Mons. Charles 

 Martin, carrying out and rectifying the ideas of Vic. d'Azir, 



