747 



of the specimens in diluted picric acid solutions, which reagent seems 

 to have a special predilection for staining the sustentacular cells, but 

 is inferior to the ordinary rapid silver method for demonstration of 

 the nerve elements. My first, and one of the most successful im- 

 pregnations of the ependymal neuroglia, was obtained from the brain 

 of a dog, so advanced in years as to be sightless and almost fangless. 

 From the sections obtained from this animal nearly all the figures in 

 the first sketch were drawn, but the results were confirmed by spe- 

 cimens from eleven other brains. 



The region examined during our study, comprised those portions 

 of the inter-brain of embryonic life, represented by the infundibulum, 

 including its anterior extension to the edge of the chiasma opticorum, 

 and the tuber cinereum, dorsally to the borders of the corpora 

 mammillaria. This region is strikingly rich in nearly all the forms of 

 neuroglia cells known to be present in the higher mammalia, and in- 

 cludes several sub-forms that have not yet been described. 



The Neuroglia of the Infundibulum. 



In some of our sections the impregnation of the ependymal 

 neuroglia is so dense that nothing can be determined besides a 

 blackened mass of interlacing rods and branches ; but in others where 

 the staining is less intense, two chief, and several sub-forms of glia 

 cells may readily be distinguished. 



1) The ependymal neuroglia fills every portions of the walls of 

 the infundibulum and may be separated into a primary and several 

 sub-varieties. The most frequent form (fig. 1, no. 1) commences at 

 the edge of the ventricular cavity by a conical or elongated body of 

 small size, often having a slight triangular projection into the lumen 

 of the ventricle. From this cell-like body arises a single stout stem 

 of slightly irregular contour, that does not divide until after the cen- 

 tral region of the infundibular wall is passed, and then branches, 

 giving off a comparative small number of rami passing to the sub-pial 

 border, there to end in a globular or flattened thickening of some 

 size. This flattened knob has sometimes the appearance of being dished 

 on its outer surface. After the first branches arise, there are occasional 

 knots developed on them, giving a coarsely beaded appearance to 

 the cell extension. 



The first sub- variety (fig. 1, no. 2), does not show the cellular 

 protoplasm with the same frequency as the primary form, thought it 

 does now and then become apparent. This class is distinguished by 

 a greater thickness and irregularity of the main stem, and by the 



49* 



