778 THE NERVOUS SYSTEM. 



THE VENTRICLES OF THE BRAIN. THE EPENDYMA AND 

 CHOROID PLEXUS. 



GENERAL CONSIDERATIONS. 



As the lymph-spaces of the pia mater and the ventricles of the brain 

 are in communication, it might be supposed that they would share alike 

 in the accumulation of fluids. This, however, is uot the case. The 

 membranes of the brain may be highly cedeniatous while the ventricles 

 contain about the normal quantity of fluid ; or, on the other hand, the 

 ventricles may be widely dilated and the pia mater unusually dry. Many 

 of these varying conditions may be understood by remembering that the 

 skull and spinal canal form a closed cavity, and that accumulations of 

 fluid in one part must be at the expense of some material occupying 

 other parts, either blood, serum, or brain tissue. It is not always easy 

 to see, however, exactly how the compensation occurs. 



There may be an unusual amount of fluid in the ventricles of the 

 brain as a result of post-mortem change ; in connection with senile or 



FIG. 511. PLATES OF BONE ix THE PIA MATER SPINALIS. 



other atrophy of the brain, or in the general vascular changes which lead 

 to osdema of the brain ; in connection with inflammation of the meninges 

 or of the ependyma; or under conditions which we do not understand, 

 as in some cases of congenital and acquired hydrocephalus. Accumula- 

 tions of fluid in the ventricles are often called internal hydrocephahis to 

 distinguish them from accumulations in the meniuges external hydro- 

 cephalus. 



INFLAMMATION. (Ependymitis.) 



Acute Epsndymitis. In this condition, which may occur by itself, but 

 is usually associated with inflammation of other parts of the brain, the 

 ependyma is congested, the vessels are more prominent than usual and 

 are often tortuous. The ependyma and the adjacent brain tissue may be 

 thickened and infiltrated with pus cells, and the surface of the ependyma 

 covered with fibrin and pus in variable quantity (Fig. 512). The cavi- 

 ties of the ventricles may contain purulent serum. Small haemorrhages 

 may also be present in the tissue of the ependyma. This, as well as 

 other forms of inflammation, is more common in the lateral ventricles 

 than in the others, but not infrequently involves the fourth ventricle. 

 The choroid plexus may participate in the inflammatory changes of the 



