586 



THE POSTERIOR PITUITARY AND THE NERVOUS SYSTEM. 



tional testimony in favor of our conception of the whole mech- 

 anism of brain-function will appear. Indeed, the canaliculi 

 are evidently the openings into the neuroglia-fibrils. But these 

 microscopical channels, which are often one-sixth the size of a 

 blood-corpuscle, would soon be blocked were the latter allowed 

 to reach them. There is interposed between them, therefore, 

 a lymphatic membrane, similar to the one which, as we have 

 seen, forms the lymph-space from which veins start. Here, 

 however, a double purpose is served, as shown in the sketch. 

 It forms two cavities: the one surrounds the blood-vessel, and 



h 



d f 



RELATIONSHIP OF THE VASCULAR AND LYMPH CHANNELS IN 

 THE BRAIN. (Andriezen.) 



a, Pia-arachnoid. 6, Brain-substance, c, Epicerebral space, d, Ad- 

 ventitial sheath. , Intra-adventitial space, f, Extra-adventitial space. 



(According to our view, these are all blood-channels: The blood arrives 

 in pial artery (g), and escapes through the walls of the latter into the 

 "intra-adventitial" space (e). Part of the plasma of this blood passes 

 through sheath d into the "extra-adventitial" space (f) and enters neu- 

 roglia- fibers and cells (h, h, h), and then passes into the apical dendrites 

 of neurons; the rest of the plasma and all corpuscles return to the veins 

 by way of the "intra-adventitial" space at c.S.) 



represents the channel connected with the venous system, to 

 which all corpuscles return; the other, or external, space re- 

 ceives only the blood-plasma which has passed through the 

 membrane. The latter, being mainly composed of endothelial 

 plates, is therefore phagocytic and bactericidal, and thus admits 

 into the neuroglia canaliculi not only plasma relieved of all its 



