22 SURGICAL APPLIED ANATOMY. [Chap. n. 



The following anatomical conditions tend to 

 minimise the effects of violence as applied to the skull : 

 The density of the scalp and its great mobility ; the 

 dome-like arrangement of the vault ; the number of 

 the bones that compose the head, and the tendency of 

 the violence to be broken up amongst the many seg- 

 ments ; the sutures which interrupt the continuity of 

 any given force, and the sutural membrane, which acts 

 as a kind of linear buffer ; the mobility of the head 

 upon the spine ; and the elasticity of the cranial bones 

 themselves. 



In children the membranous layer between the 

 sutui'es is of considerable thickness, but, as age 

 advances, this membrane disappears, and the bones 

 tend to fuse together (synostosis). The sutures begin 

 to be obliterated about the age of forty, the change 

 commencing on the inner aspect of the suture, and 

 appearing first in the sagittal suture, then in the 

 coronal and lambdoid, and last in the squamous. The 

 synostosis may be complete by the age of eighty 

 (Tillaux), and its onset is said to be coincident with 

 the cessation of increase in the weight of the brain. 

 This latter assertion is supported by the fact that it 

 appears earlier in the lower races of mankind. As 

 age advances, moreover, the skull bones become less 

 porous, and lose much of their elasticity. They are, 

 therefore, more readily fractured in the aged than in 

 the young. 



As a rule, in fracture the entire thickness of the 

 bone is involved ; but the external table alone may be 

 broken, and may even be alone depressed, being 

 driven into the diploe, or, in the case of the lower 

 frontal region, into the frontal sinus. The internal 

 table may be broken without a corresponding fracture 

 in the outer plate ; and in nearly all cases of complete 

 fracture, especially in such as are attended with 

 depression, the internal table shows more extensive 



