Chap, ii.] BONY VAULT OF THE CRANIUM. 23 



Hutchinson, and in it a fracture of the occipital bone 

 was associated with a like lesion in the cribriform 

 plate, the intervening part of the skull being un- 

 injured. (3) Fractures of the vault, and especially 

 linear fractures due to such diffused violence as 

 obtains in a fall upon the head, are very apt to spread 

 to the base. In so spreading they reach the base by 

 the shortest possible route, and without any regard to 

 the sutures encountered or to the density of the bones 

 involved. Thus, fractures of the frontal region of the 

 vault spread to the anterior fossa of the base, those of 

 the parietal region to the middle fossa, and those of 

 the occipital region to the posterior fossa. To this 

 rule there are but few exceptions. -To indicate more 

 precisely the exact bones involved in these three 

 districts, Mr. Hewett has divided the skull into three 

 zones. The anterior zone includes the frontal, the 

 upper part of the ethmoid, and the fronto-sphenoid ; 

 the middle, the parietals, the squamous, the anterior 

 part of the petrous portion, and the greater part of 

 the basi-sphenoid ; and the posterior, the occipital, 

 the mastoid, the posterior part of the petrous bone, 

 with a small part of the body of the sphenoid. 



In all fractures of the base there is usually a dis- 

 charge of blood and of cerebro-spinal fluid externally. 

 (1) In fractures of the anterior fossa the blood usually 

 escapes from the nose, and is derived from the menin- 

 geal vessels, or in greater degree probably from the 

 torn mucous lining of the nasal roof. To allow of the 

 escape of cerebro-spinal fluid from the nose, there 

 must be, in addition to the fracture in the nasal roof, 

 a laceration of the mucous membrane below that 

 fracture, and of the dura mater and arachnoid above 

 it. In many cases of fracture in this part the blood 

 finds its way into the orbit, and appears beneath the 

 conjunctiva. (2) When the middle fossa is involved, 

 the blood escapes from the external auditory rneatus, 



