The brain of Acipenser. 67 
the cephalic end of the L. lineae lateralis, in the region of the 
ventral root of the N. lineae lateralis VII. In Phots. 3 and 7 there 
is to be seen a sharp vertical ridge beneath the valvula cerebelli, 
projecting inward from the lateral wall and descending to the mid- 
ventral groove. This ridge marks the position of the commissura 
ansulata, and may be taken as the cephalic border of the medulla. 
b) Cerebellum. 
The cerebellum is shown in lateral view in Phots. 1 and 4, in 
dorsal view in Phots. 5 and 6, in median section in Phots. 2 and 3, 
and in ventral (internal) view in Phot. 7. -The lateral lobe of the 
cerebellum rises from the lateral wall of the medulla at its cephalic 
end (Phot. 4), and from the side appears bowl-shaped with its con- 
vexity cephalad. The dorsal and cephalic surface is marked by a 
deep sagittal groove which joins in Y-shape with the transverse 
groove between the cerebellum and tectum (Phot. 5). Beneath the 
sagittal groove lies the great median molecular mass of the body 
(Phot. 14), and at the bottom of the transverse groove is a deep 
transverse fissure dipping into the cerebellum (Phot. 3, compare 
Phot. 17). Of the large median mass, all that part caudal to the 
transverse groove I shall call the body; the part cephalad from this 
groove is the valvula. In dorsal view (Phots. 5 and 6) the caudo- 
lateral angles of the body are to be seen projecting slightly beyond 
the caudal border of the lateral lobes. In lateral view (Phot. 4) a 
large part of the body is visible. Seen from the lateral, and especially 
from the ventral surface (Phot. 7), the body and valvula present a 
prominent median ridge, the keel of GORONOWITSCH. This consists 
of molecular substance with scattered PURKINJE cells. About opposite 
the lateral groove between the cerebellum and the tectum, a trans- 
verse ridge is seen (Phot. 7) extending between the keel and the 
lateral wall, which probably marks the place of entrance to the 
cerebellum of the commissure of the secondary vagus nucleus 
(page 87), and part of the tractus lobo-cerebellaris (page 98, 134). A 
comparison of Phots. 3 and 4 shows a great difference in the height 
of the cerebellum with reference to the tectum and corresponding 
differences in form between the two brains. The cerebellum of the 
brain in Phot. 3 is greatly depressed and extends farther caudad. 
The same was true of the brain from which the series of sections 
used for Phots. 8—28 were made. The depressed form appears 
to be due to artificial pressure, but as the brains were hardened 
5* 
