168 CLINICAL APPLIED ANATOMY. 



MENINGEAL HAEMORRHAGE. 



Meningeal haemorrhage is called extra-dural when the blood is 

 effused between the skull and the dura mater ; sub-dural when it 

 lies between the dura and the arachnoid ; sub-arachnoid when it 

 lies between the arachnoid and the pia. 



Extra-dural haemorrhage is usually due to traumatic rupture 

 of the middle meningeal artery, and from its position gradually 

 induces compression of the adjacent motor cortex and by gravi- 

 tation also comes to compress the nerves of the middle fossa on 

 the side of the haemorrhage. 



Sub-dural haemorrhage may exist by itself or in association 

 with the other varieties. This form of haemorrhage may spread 

 widely in the subdural space and even surround the medulla or 

 spinal cord. A subdural collection of blood may come from the 

 meningeal arteries or veins, or from the great sinuses as a result 

 of their rupture. A particular variety is termed sub-dural 

 haematoma: it arises in connection with head injuries and is also 

 often associated with insanity. 



Sub -arachnoid haemorrhage may result from rupture of 

 aneurysms at the base of the brain since the trunks on which 

 these aneurysms occur are contained in the sub-arachnoid spaces. 

 Haemorrhage from the interior of the brain may also make its 

 way into the same spaces in the manner already described. 



CEREBRAL EMBOLISM. 



A constricted or ulcerated mitral valve is the commonest cause 

 of cerebral embolism. Emboli are sometimes derived from clots 

 in the recesses of the left auricle or from the aortic valves, or 

 from an aneurysm of the arch of the aorta. 



Clots from the systemic veins, large enough to produce embolic 

 softening of the brain, cannot traverse the pulmonary capillaries, 

 so when embolism accompanies thrombosis of the veins of the 

 uterus, lower extremities, or other parts, there is usually a left- 

 sided endocarditis or an abscess of lung to account for it. A 



