chap, ii.] BONY VAULT OF THE CRANIUM. 21 



particles together at the outer table and asunder at 

 the inner table. 



Fractures of the vault are due to direct 

 violence. The construction of the skull is such that 

 the fracturing force is resisted in many ways. (1) When 

 a blow is received on the vertex in the parietal region, 

 the force tends to drive the upper borders of the 

 two parietal bones inwards. Such driving in of these 

 borders must be associated with a corresponding 

 outward movement of the inferior borders. This 

 latter movement is forcibly resisted by the squamous 

 bone and the great wing of the sphenoid, which over- 

 lap the lower edge of the parietal bone. Moreover, 

 the force transmitted to the squamous bone is passed 

 on to the zygomatic arch, which takes its support 

 from the superior maxillary and frontal bones. This 

 arch then acts as a second resisting buttress, and this 

 transmission of force from the vertex to the facial 

 bones is said to be illustrated by the pain often 

 felt in the face after blows upon the top of the 

 head. (2) If the upper part of the frontal bone be 

 struck, the force is at once transmitted to the parietal 

 bones, because the upper part of the frontal bone 

 (owing to the manner in which its border is bevelled) 

 actually rests upon the two parietal bones, so the 

 same resistance is again called into action. If there be 

 any tendency for the inferior parts of the bone to move 

 outwards, as would certainly be the case while the mid- 

 frontal suture existed, such movement would be resisted 

 by the great wings of the sphenoid, and by the anterior 

 inferior angles of the parietal bones which embrace 

 or overlap these parts of the frontal. Thus it will be 

 seen that much depends upon the manner in which 

 the corresponding edges of the frontal and parietal 

 bones are bevelled. (3) Blows upon the occiput are 

 less distinctly provided for, and it must be owned 

 that a by no means heavy fall is sufficient to break 



