338 



THE MECHANICAL FUNCTIONS. 



layers, but by the application of fresh layers on the 

 outside of those already existing. 



In the flat bones, the process of ossification is 

 very similar to what I have just described ; only 

 the fibres have a radiated arrangement, shooting 

 out from the spot where the first deposit took place, 

 as from a common centre. This is seen in Fig. 

 174, which represents the parietal bone of the 



176 17A 175 



human skull, in an early stage of its ossification, 

 and sho^^s very distinctly the radiating fibres. In 

 the cubical, and more irregularly shaped bones, 

 the process is, doubtless, conducted with the same 

 order and regularity, although it cannot be so 

 readily followed by the eye. 



The same process is repeated in different parts 

 of the bone, Avherever nature has, in conformity 

 with determinate laws of developement, appointed 

 particular centres of ossification. The bone con- 

 tinues to extend from each of these centres, pro- 

 ceeding gradually towards the circumference, or 

 remoter parts of the cartilage, on which the ossific 

 materials are moulded, and by the form of which 

 that of the future bone is regulated. The process 

 of ossification has, however, this peculiarity, that 

 the cartilage is progressively absorbed to make 



