150 



tables shall be serrated, that they may mutually receive each other, 

 and thereby allow the external table of each to be reciprocally sup- 

 ported by the internal table of the other. If the external table was 

 not prolonged over the internal, there could not be any support gi- 

 ven ; and, if there was not an interlacing of the external tables, 

 there would not be a mutual support. As the circumstances, by 

 which each of the tables is affected, are different, the serrated con- 

 formation, necessary in the external table, does not exist in the in- 

 ternal ; for no advantage could be derived from their interlacing, 

 but a great inconvenience would result from it, as the internal table 

 would be thus rendered nearly unable to support the external. 



These considerations prove, not only the mechanism of the kind 

 of articulation, which exists in the vault, but also how admirably it 

 is calculated to answer the desired end. Had the bones been here 

 connected by plane surfaces, as they are in the base, they could not 

 afford any support to each other ; or had one bone overlapped the 

 other, one only would be supported, and the other easily driven in.* 



While the bones of the cranium are separated, by a considerable 

 interval from each other, I have already remarked, that they are re- 

 tained together, in the vault, partly by the dura mater and pericra- 

 nium, and partly by a very thin stratum of cellular substance, which 

 passes from the edge of one bone to the edge of another ; but, in the 

 base, by a cartilagenous substance, which surrounds the edge of the 

 growing bone, and by the membranes covering the cranium, and lin- 

 ing its internal surface. Such is, for example, the state of the cra- 

 nium at birth. In proportion as the bones are increased, this interval 

 between them is diminished, and the medium of connexion modified 

 in its nature. In the cranium of a child, about twelve months old, 

 we remark, that the very thin stratum of cellular substance, which 



* See Winslow, Mem. de I'Acad. des Sciences, 1720. 



