ON THE CHOROID PLEXUSES 59 



other openings of communication, lending themselves to 

 its accomplishment. Secretion, or excretion, being thus 

 effected within the brain by structures organically, or 

 histologically, continuous with its arachno-pial meninges, 

 would more than suggest that a like function is performed 

 by these latter, at any rate by the pial structures, and that 

 therefore the pia mater, throughout its extra- and intra- 

 cerebral and entire extent, performs the great function of 

 keeping fully replenished the extra-, inter-, and intra-spaces 

 of brain, cord, and nerves, as well as of supplying, in 

 ordinary physiological conditions, the necessities of the 

 lymph spaces of eyes, ears, and other continuous spaces. 



If this be so, the pia mater performs the double function 

 of conveying nourishment into, and through, the neuroglial 

 matrix to the central nervous system, and of maintaining 

 a fluid medium of protection and support, both within 

 and without that system, besides maintaining mechanically 

 the patency of its circulatory lymph paths. 



These neural lymph paths, or spaces, consisting of the 

 ventricles of the brain, the central canal of the cord, the 

 inter-meningeal spaces surrounding both brain and cord, 

 and the inter-neurilemmar spaces of the nerves, being, as 

 we contend, continuous the one with the other, from the 

 centre to the periphery of the nervous system, and being 

 supplied from within and from without that system by a 

 regularly formed and graduated secretion, or excretion, 

 afford a means of escape to effete and disintegrated 

 material, unequalled in completeness, extent, and adapt- 

 ability throughout the entire extent of the excretory 

 economy of the body, as well as a mechanical support and 

 bufFerage unique in its completeness and efficiency. 



On continuing our study of the histology of the choroid 

 plexuses we have been much struck with their adaptability 

 to the requirements of glandular structures, and with the 

 structural arrangement of their true glandular elements, 

 these being situated mainly on their external aspects, the 

 excreting cells acting in the manner of, and somewhat on 

 the same principle as, those of the Malpighian corpuscles, 

 or bodies, of the kidneys, the lymph, or fluid, distilling 

 through their respective terminal textures. No doubt 

 a like function belongs to, and is performed by, the 



