26 SURGICAL APPLIED ANATOMY. [Chap. in. 



the source of the bleeding in twenty-seven instances 

 (P. Hewett). The artery is most often torn, as it 

 crosses the anterior angle of the parietal bone. There 

 are many reasons for this : the bone where grooved by 

 the artery is very thin ; the artery is often so imbedded 

 in the bone that fracture without laceration of the 

 vessel would hardly be possible ; and lastly, the par- 

 ticular region of the artery is a part of the skull 

 peculiarly liable to be fractured. Failing this vessel, 

 the most frequent source of extra-meningeal haemorr- 

 hage is the lateral sinus, for reasons that will be 

 obvious. 



With regard to the blood sinuses formed by the 

 dura mater, nothing remains to be added to what has 

 been already said (page 10), except, perhaps, to 

 observe that the relations between the internal 

 carotid artery and cavernous sinus are so intimate that 

 arterio- venous aneurism has followed injury involving 

 these parts. It will be seen also with what ease this 

 sinus could become thrombosed in cases of inflamma- 

 tion within the orbit by the extension of the mis- 

 chief along its great tributaries, the two ophthalmic 

 reins. 



Sarcomatous growths, springing from the dura 

 mater or other of the meninges, may make their way 

 through the cranial bones, and project as pulsating 

 tumours beneath the scalp. Such growths are included 

 under the title of "fungus of the dura mater." 



Between the dura mater and the arachnoid is the 

 subdural space, formerly known as the " cavity of 

 the arachnoid. 1 ' According to Prescott Hewett, ex- 

 travasations of blood after injury are more common 

 in this space than in any other part within the skull. 

 The blood so poured out may become more or less 

 discoloured, and present in time the aspect of a thin 

 and peculiar membrane; or the collection may form 

 itself into a species of cyst (" arachnoid cyst ") that 



