CELL MASSES IN THE FOREBRAIN 403 
sections, sometimes obliquely to it. In the latter case they may 
extend through as many as twelve sections ten microns in thick- 
ness. When the clusters are cut either across the long axis or 
lengthwise of it, the core is almost always seen to contain a 
lumen around which the cells are arranged (fig. 35). The lumen 
is bounded by a strong limiting membrane and contains more or 
less of lightly staining material, resembling mucus. Occasion- 
ally a flattened nucleus is seen in the lumen. 
In the caudate and parolfactory nuclei these vesicles are 
found only near the ventricle except in the area where these two 
nuclei meet beneath the ventral ventricular groove. Here they 
are found farther from the ventricle, even in the deeper layer of 
the tuberculum olfactorium. In this region these vesicles lie 
adjacent to or intermingled with the islands of Calleja, to be 
described below. It was at first thought, indeed, that these 
were islands of a special type. The vesicular arrangement and 
other characters of the cells, however, differentiate these struc- 
tures sharply from the islands of Calleja. The cells are typically 
columnar and radially arranged around the lumen, the nuclei 
usually placed near the peripheral end of the cells. The cell- 
bodies are often filled with small granules unlike the Nissl-bodies 
of adjacent nerve cells. The nuclei are small, ovoid and dense, 
resembling those of ependyma cells rather than those of nerve 
cells. There are often larger cells, obviously nervous, wedged in 
among or closely applied to the outer surface of the small cells 
of the vesicles. Although the fascicles of nerve fibers in the 
caudate often pass close over the surface of these vesicles and 
sometimes diffuse fibers appear to run ventrad from a vesicle, 
I have not found in Cajal or Golgi sections fibers arising from the 
cells of the vesicles. 
I suspect that these vesicles are composed chiefly of ependyma 
cells and that their lumina represent vestiges of ventricular 
cavity which have been pinched off during development. This 
might happen owing to the thickening of the caudate and par- 
olfactory nuclei and consequent encroachment upon the ventral 
part of the ventricle. The fact that these cell clusters are not 
penetrated by the neuropile (fig. 35) and the fact that no definite 
