148 



motion. This, however, is effectually prevented by the breadth 

 of the plane surfaces, by which the bones in the base are united. 



As these few observations are sufficient to illustrate the function of 

 each kind of articulation, I shall not farther enlarge on the subject. 

 It may, however, be here remarked, that the respective functions of 

 each kind of articulation is so accurately fixed, that the nature of 

 the injury, to which particular parts of the cranium are subject be- 

 ing known, we could, a priori^ determine the kind of suture to be 

 found in each part. These observations will perhaps be considered 

 as of some importance, in consequence of their affording princi- 

 ples, by which we can explain the causes of the innumerable and 

 hitherto apparently capricious varieties remarked in tlie articula- 

 tions of the cranium. They also demonstrate the connexion, which 

 exists between their construction and the well being of a cavity des- 

 tined to protect the most important and most delicate organ of our 

 system ; and we are thereby forced to consider their formation as 

 depending on determined laws, and not on the uncertain influence of 

 pressure, or the accidental formation of radii. 



Anatomists not fully acquainted with the manner, in which the 

 true suture enables the bones that form it, mutually to support 

 each other, have been mucii at a loss to explain a peculiar appear- 

 ance, exhibited by this kind of articulation : the existence of serrae 

 only on the external surface of the cranium. The common me- 

 chanical explanation being not only entirely inadequate, but almost, 

 if not wholly, unintelligible.* 



• It must be observed, that the indentations of the sutures do not appear on the inside of 

 the cranium by much so strong as on the outside ; but the bones seem almost joined in a 

 itraiglit line : nay, in some skulls, the internal surface is found entire, while the sutures are 

 manifest without, iMch may probably be oviing to the less extent of the concave than of the convea 

 surface of the cranium, xiihereby the fibres of the internal side would be stretched Jarther out at the 



