41 
squeteague (Cynoscion regale) a considerable length (8 to 10 mm) of 
the fibre was found irregularly coiled within the 4th ventricle, that 
portion of the central canal of the cord near the ventricle, from which 
the fibre had evidently come, being empty for a length of more than 
a centimetre. In this case the roof and walls of the ventricle had 
remained intact, so that the fibre could have gotten into the ventricle 
only by a recoil due to its own elasticity when, in the fresh condition, 
the cord was cut across. This contracted and coiled part of the fibre 
was found to have a diameter of 12 «, whereas in other parts of the 
same brain and cord where the fibre was normally in place the dia- 
meter was only 6 w. All these things tend to show that the fibre in 
the fresh condition before the action of preserving fluids is an elastic 
structure probably under considerable tension. After fixing, the fibre 
is usually brittle and in cutting may be broken at some distance from 
the plane of the section. Under such conditions it breaks sharply at 
right angles to its length. Occasionally in longitudinal sections of the 
cord cutting the fibre obliquely, the fibre at the point of cutting is 
somewhat bent in the direction taken by the knife, much as a soft 
wire might be. 
The course of REISSNER’s fibres through the ventricles to its ter- 
mination anteriorly has been most thoroughly studied in Teleosts, 
where it has been followed continuously in Cynoscion, Pomatomus, 
Morone, Amia and Salvelinus. The fibre has been foilowed to its ter- 
mination in the torus also in Raja, Lepidosteus, Necturus, Alligator, 
Scelopteris, garter-snake and, less completely, in many other species 
including the mouse and pigeon. Its course is the same in all except 
in so far as it is dependent on the size and relations of the ventricles 
and other parts of the brain, which differ in different species. The 
following description applies more particularly to Teleosts, but in a 
general way to all. 
Passing out of the central canal (Fig. 12) cephalad into the 4th ven- 
tricle, and keeping near to the floor of the ventricle, REISSNER’s fibre 
runs through the narrow lumen under the lobi vagi (in Teleosts) through 
the aqueduct of Syuvıus into the 3d ventricle (Fig. 7). There is no 
variation whatever in the size of the fibre in passing from the spacious 
ventricles through the narrow aqueduct. In the ventricle of the optic 
lobes the fibre continues cephalad between the two prominences of the 
colliculi lying close to the floor of the ventricle. At the anterior end 
of the ventricle, where, as the ventricle narrows, its floor becomes 
depressed, the fibre runs ‘straight across the depression toward the 
