George L. Streeter 305 
Tig. 4 shows the floor of the fourth ventricle bounded on each side 
by the insertion of the tela choroidea inferior, the torn edge of which 
shows in the sections, situated at a point corresponding to the descend- 
ing root of the vestibularis. Lateral to it le the nuclei of the pos- 
terior columns. ‘The space between the attachment of the tela and the 
median line is divided by surface furrows into three areas. ‘The outer- 
most area consists superficially of a loose vascular tissue, similar in 
structure to the vascular area seen in sections 1 and 2. Here it cor- 
responds to the area postrema of Retzius. Median to this there are two 
other areas separated by a sharply cut furrow. The one at the median 
line forms the beginning of the trigonum hypoglossi. The smooth 
rounded area between this and the area postrema consists of a thickened 
ependyma overlying the vagus nucleus. By tracing this structure 
through the sections between 4 and 5 it is found to correspond to the 
funiculus separans. It appears in the section somewhat broader than 
in the drawing of the floor of the ventricle (Plates I and IT). This 
is due to the fact that the structure curves caudally towards the median 
line, and is therefore in fig. 4 cut in an oblique direction. A relation 
between the funiculus separans and the fasciculus solitarius, as found 
by Dejerine, is not found in any of our sections. It will also be observed 
in section 4 that the area postrema does not represent an intraventricu- 
lar part of the nuclei of the posterior columns of the cord, but is a vascu- 
lar structure overlapping the vagus nucleus, and associated in structure 
and position with the obex, tela choroidea, and the wedge shaped area 
seen in fig. 2. 
Fig. 5 forms a favorable place for the consideration of the finer surface 
structures in the floor of the ventricle. The three major areas are 
distinctly marked out. The area corresponding to the trigonum hypo- 
glossi is subdivided into a median and lateral area. Also at this level 
there exists the most marked formation of ridges and furrows, which 
give rise to the feathered appearance as described by Retzius. So here 
perhaps we can learn what these markings of the floor signify. Sec- 
tions of this region were studied which had been prepared by various 
methods. The most information regarding the histology of the mark- 
ings of the floor, however, was obtained from a neuroglia fibre series 
prepared by Weigert, and I will take this opportunity to express my 
thanks for his kindness in loaning them for use in this study. In this 
neuroglia series one finds directly beneath the ventricular epithelium 
a compact layer of neuroglia fibres, the ependyma,,and it is found to 
be this that forms the substance of the small wrinkles seen in the 
floor. They appear in sections as ridges of compact neuroglia fibres, 
