750 



of which extend long, very infrequently branched rays, studded here 

 and there with bead-like thickenings. These rays extend through the 

 gray tissues almost incredible distances, passing in the direction of 

 the basal ganglia. There is always only a single process to each 

 cellular body. 



Proceeding upward, along the borders of the walls of the ven- 

 tricle, we immediately come upon another and most beautiful variety of 

 ependymal neuroglia cell. This cell is somewhat different in form 

 from any of the familiar types that have been depicted by Retzius, 

 Koelliker, Cajal and others. The body is fairly large, of a rounded 

 or flattened shape (7, fig. 1), is situated along the margin of the ven- 

 tricular cavity, and very often sends out a single short spiked pro- 

 cess into the ventricle. Out of the body very numerous lateral rays 

 proceed, extending along the margin of the ventricle, running over 

 considerable distances. From that portion of the cell body directed 

 toward the cerebral substance, grows a main process, which is pri- 

 marily single, though later it may divide into two or even three main 

 branches. This vertical process has projecting from its sides, large 

 numbers of rectangular lateral tentacles, some quite short, others of 

 medium length, similar to those passing from the body of the cell, 

 and having the same general direction. Some of these extensions are 

 thicker and shorter than the others, and have knotty and prickly 

 projections from their margins, while others are longer, and have the 

 prickles, but no knobby thickenings. Subdivisions of the lateral pro- 

 cesses are somewhat rare, but do occur. Out of the uppermost por- 

 tion of these strong vertical processes, we can almost always find a 

 long almost smooth hair-like prolongation, which shortly bends down- 

 ward toward the floor of the brain, where it meets the uptending 

 fibres of the sustentacular glia cells arranged along the inferior margin 

 of the floor, as well as the rays from the last described variety of 

 cell, and mingling with them, is soon no longer distinguishable in the 

 dense meshwork, though it is probable from the appearance of a few 

 isolated examples, that they all end with a ball-swelling against the 

 pial limit. The general effect given by these ventricular cells reminds 

 one strongly of a lateral view of some of the varieties of conifers, 

 hence we have named them the fir-tree ependymal cells. 



These very beautiful bodies are thickly set along the border of 

 the ventricle, and are found in perfection up to a height of several 

 millimetres above the debouchment of the ventricle into the infundi- 

 bular cavity, above which they become less frequent, and are dis- 

 located (8, fig. 1) from the immediate border of the ventricle, appear 



