412 Anatomy Applied to Medicine and Surgery. 



longitudinal sinus ; whereas, the posterior branch lies on 

 the posterior part of the squamous and then on the corre- 

 sponding portion of the parietal. This vessel is the prin- 

 cipal source of extra-dural haemorrhage. Hewett found 

 that the middle meningeal was involved in twenty-seven 

 out of thirty-one cases of this condition. Fracture of the 

 skull generally causes injury to the artery from the sharp 

 edge of the bone lacerating the vessel, especially when it is 

 contained in a canal, as above mentioned, although Jacob- 

 son showed, that in eight cases out of seventy, in which 

 the middle meningeal was affected, there was no fracture. 

 In these cases it is probable that the sudden alteration in 

 tfce shape of the skull that results from violent injuries 

 may overstretch and so rupture the vessel without pro- 

 ducing a fracture of the bones. It is in extra-dural 

 haemorrhage that relapsing unconsciousness so frequently 

 occurs, since, when the vessel is torn, the patient may re- 

 cover sufficiently to go about for a few hours, or even 

 longer, before the blood, pouring out from the injured ves- 

 sel, will compress the brain sufficiently to induce coma, as 

 in a recent case, where the batter in a baseball game struck 

 a man, who was intoxicated, on the head. The latter 

 walked around for an hour or two and then fell asleep, so 

 his friends thought, in which condition he was removed to 

 his home, still under the belief that he was drunk. He 

 died that night, and at the post-mortem fully a half-pint 

 of blood was found between the dura mater and the skull. 



