lyS Journal of Comparative Neurology. 



The brain cells, proper, are connected with the exterior and with 

 each other, by both direct and indirect methods. They have 

 two or more branching fibres or poles, through which their con- 

 nections are effected. Some of the cells have a basal process 

 which does not diminish in size and has in some instances been 

 connected directly with an axis cylinder of an efferent nerve 

 filament. The other processes diminish gradually in size by 

 subdivision until it is very difficult to trace them to their termin- 

 ation. They seem finally to form a delicate matrix of fibrils, 

 and many of the cells have no distinctive processes other tlian 

 those which form this matrix. From the aggregation of the 

 fibrils of this matrix on its ventral side larger fibres arise which 

 have been traced into the axis cylinder of other nerve fibres. 

 Whether or not this diff'erence in the connection of the bram 

 cells with the axis cylinders of the nerve fibres indicates a differ- 

 ent function in the two classes, is not well determined, but anal- 

 ogy would indicate that it does so, and it has been assumed that 

 the direct connection is with efferent nerve fibres and the indi- 

 rect with afferent fibres. 



The blood vessels to the central cortex are exceedingly del- 

 icate in structure and are susceptible of great variatioi in 

 diameter. In the capillaries the various coats disappear, leaving 

 the endothelial lining alone, and this is quite delicate in struc- 

 ture. 



The blood vessels lie in a lymph space, which is much larger 

 than the diameter of the vessel and is probably lined with a del- 

 icate membrane which closely invests the brain tissue. About 

 the brain cells there is a similar lymph space and these peri-vas- 

 cular and peri-cellular lymph spaces have been seen to be con- 

 nected by lymph tracts or clefts in the brain substance, which 

 thus afford a direct drainage of the cell surfaces into the great 

 lymph reservoirs between the membranes of the brain. Along 

 the course of the vessels and in the neighb^rhoid of the cells, 

 most delicate and almost indiscoverable (in the normal state) 

 cells are found which are sometimes connected to the vessel and 

 reach out toward the cell elements. In pathological states these 

 become much more visible, increase ^in size, are more readily 

 stained, and become filled with the products of cell degenera- 

 tion. 



