'in (he HkidU of Jiii/iuih. 22S 



bone was easily separable irom the general 

 •piass, ^pd formed a thin layer externally, af- 

 fording one of the best prodfs I have met with, 

 of the hicrease of cylindrieal bones in thickness 

 by deposition externally, whiilst a correspond- 

 ing internal absorption goes on. From tlie 

 striking similarity of appearance on the surfaces 

 and edges of the bones, we may safely con- 

 clude, that the same process of deposition was 

 going (^n in both, and may thencq infer, that 

 the bone^ of the skull ar^^ increased in extent 

 by the .ije posit ion of osseous matter at thck 

 edges, or where they are joined to each other 

 by suture. This fact points out to us, in a 

 great measure, tlie rciil use of this peGuli;ir 

 mode of junction. 



In oider that the bones of the skull may. be 

 increased in extent, it is necessary that they 

 should be retained at a certain distance from 

 each other ; that the periosteum with, its vessels 

 may pass down bet wcetitbeni, free from com- 

 pression and secrete the osseous matter. At 

 ,the ^saiiie time, the tliin bones composing the 

 upper part of the skull, resting as an arch upon 

 its basis, must be united together so firmly, as 

 not to be separated by common degrees of 

 violence. For this purpose, projecting |)oints 

 from the external surface of each bQne,.ijLre reci- 

 procally received into corresponUiugnhche&i 



s s 



