The brain of Acipenser. 113 
similarity of size and form. They are ovoid or pyramidal cells 
measuring 10—18 by 16—32 u. They are situated near the central 
cavity (except those far forward on the outer surface which have not 
been impregnated and 
are not included in 
the description), and 
their dendrites which 
are relatively short 
and simple are di- 
rected outward. The doe Ar 
neurites arise usually 
from the basal part of 
KEN gldp. 
XEN 
GK fy 
= 1.olf-h Wy, ES 
one of the dendrites. pale lb GE 
7 Nb M. 
; N nant, ZZ KY 
The cells can be di- GE, Clongbdl. = 
NY 
videdintothree groups fir jy ( 
according to the course ! Ze \ 7, SX 
of the neurites. The dé ‘4 Gi pa 
cells in the middle At 
part of the region send Be 
their neurites caudo- 
ventrad. The fibres are coarse and straight, form a diffuse bundle nearly 
parallel with the bundle of MEYNERT, and end in the corpus mam- 
millare. This destination of the neurites indicates that the cells in 
question form the nucleus anterior. There end in this nucleus 
numerous fibres of the optic nerve (Pl. 13) which are readily seen 
in sagittal sections. The greater part of the fibres of the common 
longitudinal bundle also seem to end in this nucleus. These fibres 
may have their origin in part in the tectum, but come largely from 
the epithelial cells of the epiphysial sac as described above. 
\ The cells in the caudal portion of this region lie immediately 
| cophato-ventrad from the tectum and surround the bundles of Mry- 
NERT as they descend from the ganglia habenulae (Pl. 13). The 
group of cells is difficult to study, since there is nothing to separate 
them from either the tectum or the central grey of the thalamus. 
However, there are a number of cells somewhat closely grouped 
which send their neurites into the common longitudinal bundle in the 
direction of the tectum, in which they probably find their endings. 
From its position I shall call this the nucleus praetectalis. I have 
been wholly unable to determine the source of the fibres which end 
in it. 
P i Jahrb, XV. Abth. f. Morph. 8 
