364 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



The most powerful of the ventral commissural systems is, no 

 doubt, that of the commissure/, transversa Halleri, which is situated 

 for the most part in front of the ganglia habenulm, 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-Ruckhard, 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 ot 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. 



5.-THE SPINAL CORD. 



I 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. 1 A gradual 



i Zeit. wiss. Zool. XVIII., PL I., Fig. 4. 



