FBACTUBES OF THE BASE. 107 



case the external table will be elevated over a more extensive 

 area than the internal. 



Fractures of the Base. Fractures of the base of the skull 

 may be the outcome of direct or indirect violence. A linear frac- 

 ture of the vault may run down into the base. 



Almost every fracture of the base is open, through the mucous 

 membrane covering a large proportion of the bones entering into 

 its formation. Thus a fracture of the anterior fossa may com- 

 municate with the external air through the mucous membrane of 

 the nose ; a fracture running across the petrous portion of the 

 temporal bone through the mucous membrane lining the tym- 

 panum ; and a fracture of the posterior fossa through the mucous 

 membrane lining the roof of the pharynx. It will thus be seen 

 that in many of these fractures the meninges of the brain may 

 be put into direct communication with air that may be septic, 

 and meningitis is therefore apt to follow these fractures. 



Further, the same fact of laceration of the soft tissues cover- 

 ing the bones leads to the escape of blood from the nostrils, into 

 the tissues of the orbit, through the ears, down the pharnyx, and 

 into the muscles of the back of the neck. Likewise, cerebro- 

 spinal fluid may pass through the same channels. Again, the 

 exit of the cranial nerves through the base of the skull explains 

 the great frequency with which they may be involved when frac- 

 tures in this region occur. Thus it is, that the three cardinal 

 symptoms or signs of a fracture of the base of the skull, that is to 

 say the loss of blood, the loss of cerebro-fluid and the primary or 

 secondary injury to the cranial nerves, are dependent upon 

 strictly anatomical reasons. 



Fractures involving the anterior fossa may give rise to haemor- 

 rhage from the nose when the cribriform plate of the ethmoid is 

 damaged, or the passage of blood into the tissues of the orbit, 

 leading to subconjunctival hemorrhage or even proptosis, when 

 the orbital plate of the frontal bone is fissured. The nerves 

 which may be involved in this fossa are the olfactory, inter- 

 ference with which it is difficult to demonstrate, and the optic, 

 damage to which is apparent from the blindness which occurs. 



