THE NERVOUS SYSTEM. 777 



inal quantities of serum found after death. The veins of the pia mater, especially in 

 the posterior region, may be greatly distended with blood after death, without pre- 

 existing disease; and the intermeningeal space may contain much fluid urder the sanv 

 condition. 



HEMORRHAGE . 



Haemorrhages may occur from injury in connection with severe con- 

 vulsions, or general diseases such as the hsemorrhagic diathesis, scurvy, 

 smallpox, etc. The haemorrhages under these conditions, except from 

 injury, are not usually extensive. But in some cases of injury or 

 cerebral apoplexy, from the bursting of aneurisms of the basilar or 

 vertebral arteries, or in cases in which we cannot find a cause, a very 

 large quantity of blood may collect between the dura and pia mater, 

 and in the meshes of or beneath the latter. 



INFLAMMATION. (Meningitis.) 



Acute exudative spinal meningitis occurs under essentially the same 

 conditions and with essentially the same post-mortem appearances as 

 acute cerebral meningitis, though it is less frequent. The exudate is 

 apt to be most abundant in the posterior portions. It may be asso- 

 ciated with a similar inflammation of the pia mater cerebralis, and the 

 inner surface of the dura mater may be involved. The disease may be 

 circumscribed, but usually affects the entire length of the membrane. 



Chronic spinal meningitis is not infrequent, manifesting itself in the 

 formation of larger or smaller patches of new connective tissue or in 

 thickenings of the pia mater. The pia and dura mater may thus be firmly 

 united in places by adhesions, or the pia mater may become closely ad 

 hereut to the substance of the cord. 



Not very infrequently large numbers of pigment cells are found in 

 the pia mater spinalis, sometimes givaug it a distinct gray or blackish 

 color. 



Tuberculous inflammation is usually associated with a similar condition 

 of the pia mater cerebralis, in which case the lesion is most marked in 

 the upper portions of the cord ; but it may extend over the entire mem- 

 brane. The conditions under which it occurs and the character of the 

 lesions are similar in both. 



TUMORS. 



Fibromata, myxomata, sarcomata, and endotheliomata have boen found. 

 Small plates of cartilage and bone (Fig. 511) are sometimes found in 

 the pia mater. 



PARASITES. 

 Cysticercus sometimes occurs in the meshes of the pia mater. 



