146 



Hence, it may be presumed, that, as the cause, which produces the 

 overlapping- in one situation, produces it in others ; and, as this cause 

 is certainly in many situations not mechanical, it may be inferred, 

 that it is not mechanical in any. 



Secondly. If the serrated appearance of the true suture was 

 caused by the accidental union of the ossifying radii, it should be 

 found, in all situations, where the radii exist at the commencement 

 of ossification ; and, as the appearance of the radii is, hi all situa- 

 tions, the same, the serrated suture should, every where, have the 

 same form. Neither of these, however, is the case. 



Thirdly. Neither mechanical pressure, nor the pre-existence of 

 radii, would explain the cause of the form observable in the edges 

 of the bones in other situations ; in the base, for example, where 

 they meet by plane surfaces. 



Fourthly. There is no reason to suppose, that the cause of the 

 conformation of the articulating surfaces of the bones of the cranium 

 is diffeient from that, which determines the form of the articulations 

 in other parts of our skeleton ; and, as it is universally admitted, 

 that these depend on the laws of our organization, and not on any 

 accidental mode of ossification, or on mechanical pressure, it is much 

 to be wondered, that physiologists should have, for so long a time, 

 attributed the nature of the articulations of the cranium to such 

 causes. 



Finally. The admirable adaptation of the edges to their uses, 

 which, I shall just now prove, must immediately force us to con- 

 clude, that their construction depends on some immoveable law of 

 nutrition ; and not on the uncertain influence of mechanical pres- 

 sure, or the accidental formation of radii. 



I shall not now take into consideration the advantages arising 

 from the craniinn being composed of a great number of bones. 



