CHAPTER IX. 



VARIABILITY OF THE SKELETON. 



Reasons which have caused the skeleton to be considered the least variable 

 part of the organism Proofs of the yielding nature of the skeleton 

 during life under the influence of the slightest pressure, when long con- 

 tinued Origin of the depressions and projections which are observed 

 in the skeleton Origin of the articular surfaces Function rules the 

 organ. 



ANY one who examines the skeleton of an animal, and holds 

 iu his hands its osseous portions as hard as a stone ; who knows 

 how these bones have survived the destruction of all the other 

 organs, and how they can remain, after the lapse of thousands 

 of ages, the only vestiges of extinct animals, may naturally look 

 upon the skeleton as the unchangeable part of the organism. 

 This skeleton, he argues, is the framework of the body, and 

 the soft parts are grouped around it as best they may, reposing 

 in its cavities, spreading over its surfaces, but alwaj's obey- 

 ing a law stronger than their own, and arranging themselves 

 in the spaces which have been allotted to them among the dif- 

 ferent portions of the bony structure. 



The observer, however little he may be acquainted with 

 anatomy, _soon perceives on the surface of the bone a thousand 

 curious details ; he sees there numerous small hollows, little 

 abodes which seem to have been destined to receive or to shelter 

 some organ that has disappeared. These hollows correspond 

 with the origin of the muscles which adhered at these points to 

 the excavated bones. Elsewhere there are deep rounded grooves 

 which remind one of the channels found in the curbstones of 

 ancient wells. A cord has also passed in that direction ; it was 

 the tendon of a muscle which incessantly glided along that bone. 

 But at the two extremities of this humerus the bone is polished 

 as if by friction ; in the upper part it is rounded like a 

 sphere, and it is lodged in a cavity of the shoulder-blade which 

 it exactly fits. One would say that the movement of these 



