THK XKRVOUS SYSTEM 



429 



ventricle. The subarachnoid space communicates with the lymphatic 

 spaces within the nerve sheaths. It is also stated that it communi- 

 cates with the lymph spaces contained within the vascular connective 

 tissue (media and adventitia) of the blood-vessels which penetrate 

 the central nervous system. Whether there is normally a peri- 



3 



•c 



o 



(0 



o 

 o 



vascular lymph space between adventitia and ghal membrane is 

 doubtful and the existence has also been denied, by good authorities, 

 of lymph spaces within the glia, the gUal membrane forming in normal 

 conditions a continuous structure. The inner lamellae of the pia are 

 more loosely arranged, are more cellular and more vascular. Espe- 



