The brain of Acipenser. Tel 
munication (98b, p. 586) I stated that. the fibres of the deep de- 
scending tract became arcuate fibres to the opposite side of the 
medulla. Further study has convinced me that this statement was 
founded on insufficient evidence. Although some of these fibres ma y 
may cross the median line, I have no positive evidence that any 
of them do so. I now believe that the root fibres end in the in- 
ternal part of the acusticum and that the arcuate fibres which I have 
found are all neurites of cells in the acusticum. 
The ascending tract runs cephalad near the central cavity and 
enters a group of cells which I have called in my previous paper 
the nucleus of the median trigeminus. This nucleus is situated at 
the junction of the acusticum with the cerebellum, is directly con- 
tinuous mesially with the granular layer of the body of the cere- 
bellum and laterally with the acusticum and the granular layer of 
the lateral lobe. A large part of the trigeminus fibres pass through 
this nucleus into the body of the cerebellum. The nucleus has 
the same structure as the acusticum, except that it contains no 
PURKINJE cells. 
Tuberculum acusticum. — This is the center for a part 
of the V, VIII, and lateral line nerves. A short distance cephalad 
from the calamus there appears in transverse sections dorsal to the 
X roots an area consisting of coarse medullated fibres and cells. 
Following it forward, it soon comes to be surmounted by a cap of 
very fine non-medullated fibres. The coarse structure is the tuber- 
culum, the cap of fine fibres is the cerebellar crest of GORONOWITSCH. 
The general relations of these structures are shown in Phots. 8—15. 
In the region of the vagus and glossopharyngeus the acusticum is 
separated from the spinal V tract by the roots of those nerves. 
Between the several roots, however, there are to be seen in both 
frontal and sagittal sections, neurites and dendrites of cells in the 
acusticum extending ventrad to the spinal V tract. The neurites do 
not join the spinal V but form a bundle of fine fibres closely overlying 
that tract. These probably constitute at least a part of the fibres 
which end in the lower olive. The acusticum steadily grows larger 
as it continues cephalad. About 0,5 mm cephalad from the glosso- 
pharyngeus a large nerve of coarse medullated fibres enters the 
acusticum immediately beneath the cerebellar crest (Phot. 11). This 
is the N. lineae lateralis X. Farther forward the VIII and the 
ventral portion of the N. lineae lateralis VII enter the acusticum 
near together (Phot. 12). Cephalad from this point the acusticum 
