150 JULIA WORTHINGTON. 
brain. Bundles of fibres of the fore brain tracts run between 
these strands of cells. 
The optic nerve enters the ’tween brain, as has already 
been mentioned, through a protuberance on its ventral 
surface. It is a small nerve, with fine, straight, deeply 
staining fibres. Upon entering the ’tween brain its fibres 
take a medio-dorsal direction, at an angle of about 45° to the 
floor of the brain. They are easily followed as far as the 
chiasma, which lies at the ventro-cephalic angle of the post- 
optic decussation. So closely applied is the chiasma to the 
decussation, that it is only by the different direction of the 
fibres,—those of the decussation running parallel to the base 
of the brain, and at right angles to its long axis,—that it can 
be distinguished from it. After the crossing the fibres no 
longer remain in the compact bundle in which they entered 
the brain, but separate into a loose strand, and are directed 
caudo-dorso-laterad through the post-optic decussation. 
Beyond this they separate still more from each other, 
running singly or in small groups, and consequently are 
quickly lost among the numerous other fibres of this part of 
the brain. 
The Infundibular Process, Hypophysis, and Sacecus 
Vasculosus. The infundibular process is, as has already 
been mentioned, attached to a stalk in the median line, 
situated about two thirds of the way from the cephalic to the 
caudal end of the base of the ’tween brain. The process 
itself is about 1°35 mm. long, 1:12 mm. wide, where the stalk 
enters it, and ‘22 mm. thick. Its cavity is continuous with 
that of the infundibulum, and is lined with ependyma cells. 
These cells are of the cylindrical variety, and have long, 
stout processes, generally continuous with the long axis of 
the cell, but which may be deflected slightly from it. The 
cavity is lined with a single layer of the cells, set very close 
together, their long axes at right angles to the plane of the 
floor, and their processes coming from the end farthest from 
the cavity and penetrating through the wall to its other side. 
Under a magnification of forty diameters a section of the 
