CHAPTER IIL 



THE CRANIAL CONTENTS. 



THE membrunes of the brain. The dura 



mater, from its toughness, forms an excellent protec- 

 tion to the brain. It is very intimately adherent to 

 the bone over the whole of the base of the skull, and 

 consequently in this situation extravasations between 

 the membrane and the bone are scarcely possible. 

 Over the vault its attachments are comparatively loose, 

 although it is more closely adherent along the lines of 

 the sutures. This lax attachment allows large hsemorr- 

 hagic and purulent extravasations to collect between 

 the dura mater and the bone. Such extravasations 

 usually lead to compression of the brain, and it may be 

 noted that in the great majority of all cases of com- 

 pression the compressing force is outside the dura 

 mater. Thus, in uncomplicated cases, when symptoms 

 of compression come on at the time of an accident, the 

 cause is probably depressed bone ; when they appear 

 after a short interval, the cause is probably extrava- 

 sated blood between the membrane and the bone ; and 

 when a long interval (days or weeks) has elapsed after 

 the accident, the cause is probably a collection of pus 

 in the same situation. 



Sir C. Bell pointed out that the dura mater of 

 the vault may be separated from the bone by the 

 vibration produced by a blow. " Strike the skull of 

 a subject with a heavy mallet ; on dissecting you find 

 the dura mater to be shaken from the skull at the 

 point struck. Repeat the experiment on another sub- 

 ject, and inject the head minutely with size injection, 

 and you will find a clot of injection lying betwixt the 



