UNDEPEESSED FEACTUEES. 105 



Compression of the brain, due to haemorrhage occurring within 

 the cranium but external to the dura mater, is most commonly 

 associated with a linear fracture across the anterior inferior angle 

 of the parietal bone. At this spot the inner surface of the bone 

 is grooved by the anterior or larger branch of the middle 

 meningeal artery, the main trunk of which having entered the 

 skull through the foramen spinosum soon divides into two branches. 

 (Fig. 6.) It is rare to get haemorrhage from the trunk itself. 

 Occasionally the anterior branch lies in a complete canal rather 

 than in a groove. When a fracture occurs, the artery lying upon 

 or rather somewhat in the fibrous tissue forming the dura mater 

 may be torn. Blood is then effused between the bone and the 

 membrane, depressing the latter inwards so as to compress 

 the cerebral substance. It will thus be seen that the blood 

 poured out is sub-cranial but extra-dural, and it is better not to 

 speak of it as a meningeal haemorrhage. The extent to which 

 the blood strips up the dura mater from the inner surface of the 

 bone is limited below by the firm attachment of the membrane 

 to the base of the skull, but above only by the want of force with 

 which the blood is thrown out. The amount of blood, however, 

 which collects immediately internal to the site of the fracture is 

 quite sufficient to cause such compression as in most cases to 

 bring about hemiplegia and later coma. 



When the bleeding point has been exposed by the removal of 

 the overlying bone at the pterion, it is as a rule impossible to 

 pick up the artery with a pair of pressure forceps, because of its 

 being somewhat embedded in the tissue forming the dura mater. 

 It is therefore necessary to carry a ligature by means of a curved 

 needle into the membrane and beneath the artery in order to 

 secure it. 



When the vessel lies in a complete bony canal, a further 

 difficulty will be encountered in arresting the haemorrhage, and 

 it will then become necessary either to remove the bone carefully 

 from around the artery, or to plug the canal by means of a spicule 

 of bone or some material such as aseptic wax. 



Depressed fractures of the skull are as a rule the outcome of 



