CHAPTER VIII. 



DISEASES OF THE NERVOUS SYSTEM. 

 THE MENINGES. 



Inflammation may involve both the cerebral and spinal 

 meninges, or either separately. The dura alone may be affected 

 pachymeningitis ; the pia and arachnoid are usually affected 

 together leptomeningitis, or simply meningitis. 



In the cord, however, all three membranes are commonly 

 involved at the same time, together with the periphery of the 

 white matter of the cord itself, with which the meninges are 

 intimately connected. 



Pachymeningitis : In the brain inflammation of the outer 

 layer of the dura pachymeningitis externa is generally 

 secondary to disease or injury of the bones of the skull, of 

 which it forms the periosteum. The inflammatory process is 

 usually suppurative and confined to limited areas, though it 

 may extend to the other membranes and the brain. 



A suppurative pachymeningitis interna is generally asso- 

 ciated with a leptomeningitis or a pachymeningitis externa. 



In chronic pachymeningitis there is a diffuse or circum- 

 scribed thickening of the membrane, which is abnormally 

 adherent to the cranium and to the arachnoid, and not infre- 

 quently an ossification of the outer layers of the membrane 

 takes place. 



Hemorrhagic pachymeningitis, or hsematoma of the dura, 

 occurs especially in chronic alcoholics and the insane. The 

 condition is looked upon as a hemorrhagic inflammation of 

 the dura. There first forms a highly vascular subdural 

 pseudo-membrane, extending over the greater part of one or 

 both hemispheres, the hsematoma resulting secondarily from 

 rupture of its vessels. This pseudo-membrane presents the 

 appearance, microscopically, of granulation-tissue, and contains 

 many thin-walled bloodvessels. 



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