147 



For the present, however, it may be admitted, that this conforma- 

 tion was necessary ; and hence it became indispensable, that the 

 several bones should be vmited in such a way as to remove, as 

 much as possible, every kind of inconvenience likely to arise from 

 such organization. This appears to be the principle, which re- 

 gulates the form of the edges of the bones. How well the arti- 

 culations of the cranium are calculated to answer this end will ap- 

 pear fiom a consideration of the mechanism of this cavity in resisting 

 injury. 



If any pressure be made on the anterior, posterior, or lateral part 

 of the cranium, so as to act directly on the base, it resists in con- 

 sequence of the mutual support, which the bones afford each other, 

 by means of the broad and plane surfaces, with which they are 

 united. This mode of articulation is, therefore, peculiarly well 

 adapted to the base ; for, if the bones were here united in such a 

 manner as either to overlap, or with narrow edges mutually to 

 receive each other, they would not be able to oppose the necessary 

 resistance. 



If the top of the vault be pressed on by the fall of a heavy body, 

 by the weight of a load placed on the head and acting perpendi- 

 cularly, or by any broad and resisting body impelled against it, the 

 motion is divided and propagated in all directions. The portion of 

 the impulse, which acts perpendicularly, tends to drive in the part 

 pressed on ; but this is effectually prevented by the serrated form of 

 the articulations of the bones in this part, by means of which they 

 are enabled mutually to receive and support each other : and that 

 portion which acts laterally, tends to drive outwards the lower 

 part of the parietal bones ; but, as they are overlapped by the 

 sphenoid and temporal bones, which fonii to them a kind of buttress, 

 this cannot take place, unless these bones perform a revolutionary 



x2 



