142 



parts of the walls of the cranium, the rudiments of the future 

 bones, is subject to some variety, owing to the occasional for- 

 mation of those little bones called Wormian ; but, 1 believe, with 

 the exception of these, twenty-six will in general be found.* 



These bony nuclei are necessarily, at first, separated from each 

 other by a considerable interval ; and are held in contact, in 

 the base, by the cartilage which surrounds them, and by the 

 membrane that lines their internal and covei-s their external sur- 

 faces; but, in the vault, merely by the membranes and medium, 

 which connects these membranes. By degrees, the nuclei encrease, 

 both in thickness and superficies, so as to diminish the interval, 

 which at first existed between them. This increase is much 

 more rapid in the base than in the vault. However, even here, 

 and in those skulls which grow most rapidly, there are very few, if 

 any, of the bony nuclei brought into contact before the sixth 

 month after conce|)tion. 



At birlli, ossification is so far advanced, that almost all the 

 bones in the base are in contact with each other ; and any 

 mterval, that exists between them, is filled up by the cartilage 

 surroxinding their edges ; but, in the vault, there are few places 

 where t!.e edges of the bones are contiguous; being, in aiuiost 

 every part, separated by an interval, in some situations of consi- 

 derable extent, and connected by the dura mater and pericra- 

 nium, which line their internal, and cover their external sur- 

 face-. There is also a very thin stratum of cellular substance, 



• The frontal is formed by two, the occipital by four, the spheroidal by three, the 

 ethmoidal by three, each temporal by three, each parietal by one, and each of the small 

 bones of the ear generally by one. 



