364 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
The most powerful of the ventral commissural systems is, no 
doubt, that of the commissura transversa Halleri, which is situated 
for the most part in front of the ganglia habenule, although part of 
it is represented, receiving contingents from the inferior lobes and 
optic thalami, in Fig. 17. In Fig. 15, other commissural fibres are 
seen higher up on a level with the peduncular strands, these appear 
to belong to the commissura horizontalis of Fritsch. 
Figs. 18, 19, 20, represent sections through different planes of the 
fore-brain, and confirm the views of Stieda and Rabl-Riickhard, that 
the secondary fore-brain is not formed of two solid masses as generally 
described, but that these—the lobi anteriores or cerebral hemi- 
spheres—are nothing but raised ganglia developed in the floor of a 
great impair ventricle, the ventriculus communis, the anterior out- 
growth of the third ventricle. Each lobus anterior may be described 
as formed of a medial and lateral part. The latter becomes especially 
distinct behind (Fig. 18), and indeed its tip (CHL), Fig. 17, projects 
further back than the boundary between the secondary and primary 
fore-brain. Within the medial part of the lobus anterior, near its 
junction with the lateral, are situated the peduncular strands. In 
front of the commissura transversa the fissure of the ventriculus 
communis separating the anterior lobes extends so deep as to leave 
in parts very little to connect them, but ependyma and pia. The 
optic tracts, however, soon replace the commissura transversa, and 
bind the ventral surfaces of the anterior lobes together. (Fig. 18.) 
In front of this where the optic chiasma merely rests on the ventral 
surface of the brain, the lobes are joined by the commissura anterior. 
In its posterior planes this is formed of fibres of two different 
characters, which give place in front to the ordinary grey matter of 
the anterior lobes. Still further forwards where the olfactory tracts 
are given off (Fig. 20), the lobes are widely separated, and lie free 
within the cavity of the ventriculus communis, except for a small 
place on the ventral surface of the olfactory tracts. This attachment 
persists in front, where the ventriculus communis has been sub- 
divided into the ventricles of the olfactory tracts as described above. 
B.—THE SPINAL CORD. 
T have not devoted any special study to the spinal cord. Sections 
in the anterior region resemble in the arrangement of grey and white 
matter the condition in Silurus as figured by Stieda.’ A gradual 
1 Zeit. wiss. Zool. XVIIL., Pl. I., Fig. 4. 
