149 



If we consider the function of this suture, which is to enable the 

 bones, that form it, mutually to receive and support each other; 

 and the; manner, in which the conformation of their edges perform 

 this office, the appearance is easily explained. The bones of the 

 cranium are composed of two layers or tables, an external and an 

 internal. In the serrated suture, the external table of each bone is 

 applied on the internal of the other, in such a way, that the latter 

 supports the former. It is therefore necessaiy, that the external 

 table of both bones be mutually prolonged over the internal, upon 

 which they lie, and from which they receive their support. This is 

 accomplished in tlie following nmnner. A number of serrae or pro- 

 cesses belonging to the external table of one bone, for example, of 

 the right parietal, pass into cavities or fissures for their reception, in 

 the external tai>le, and on the internal table of the opposite bone, or 

 left parielal ; while, in return, an equally great number of serrse of 

 the left parielal pass into cavities for their reception in the external 

 table and on the internal table of the right parietal. It is easy 

 to apply these observations to explain the cause of the existence 

 of the serrai externally, and consequently of their absence inter- 

 nally. Thus, we have seen, that, in this kind of articulation, 

 the internal tables support the external. Now it is necessary, 

 first, that the external table shall be prolonged over the internal, 

 from which it receives support ; secondly, that the external 



edges of the bones than the exterior ones, if they were not resisted. The resistences are the 

 fibres of the opposite bone, the parts within the skull, and the Diploe; of which the last being 

 the weakest, the most advanced fibres, or serrse, run into it, and leave the contiguous edgei 

 equal, and more ready to unite : whereas the serrae of the external table have space enough 

 for their admission between the fibres of the opposite bone ; and, therefore, remain in the 

 indented form, and are less liable to the concretion whereby the sutures are obliterated. 

 Monro's Woiks, edited by his ion, p. 76. See also Huuauld, Mem. de I'Acad. dcs Scieocee, 

 1730. 



