144 Cincinnati Society of Natural History. 



hippocampal region, Fig. 8, Plate VIII., and seems to embrace 

 the continuation of the olfactory tract. The tract connecting the 

 median flask-cell area with the small multipolar cells of the lower cor- 

 tex, continues forward more than half the length of the hemispheres, 

 and its fibres pass chiefly, but not solely, to the ventricle side of the 

 cell layer. As these flask-cells are traced backward they increase 

 in number, and underlie the dorsal motor cell-layer upon the occip- 

 ital region. 



The fourth cell-area occupies the ventral or inferior aspect, and 

 consists of small multipolar, very irregular, and deeply stained cells, 

 reminding of the cells of the olfactory lobe. These cells are irreg- 

 ularly clustered as in the corresponding region of mammals. The 

 connection with the third area has already been noted. The axial 

 direction of the cells is not uniform, but the apical processes of the 

 pyramidal dorsal (motor) cells are mainly peripheral; elsewhere 

 the cortical belt is so thin that the cells are nearly parallel to the 

 surface, and the relations are difficult to make out. It seems, how- 

 ever, that the axial positions of the two principal varieties are 

 never parallel. 



Description of a section through the anterior commissure. The sec- 

 tion (Plate VIII., Fig. 9,) passes through the chiasm, and exhibits 

 the anterior part of the thalamus where it narrows to form the 

 peduncles of the fore-brain. The chiasm consists of fibre clustres 

 interlocking as the fingers of the folded hands. The fourth ventri- 

 cle has a transverse expansion above the chiasm, and extends 

 upward as a narrow slit to the anterior commissure. The region 

 dorsad to the lower expanse of the ventricle is crowded with small 

 angular cells of the olfactory type, and seem to be connected with 

 the dense latero-basal clusters by fibre tracts. From this region 

 there ascends to the commissure a definite tract passing through 

 the loop formed by the callosum. The cells on either side 

 of this tract dorsally are of the pale, flask-shaped type. The 

 commissura anterior consists here of a transverse band of distinct 

 fibres passing to the part of the peduncular fasciculus where fibres 

 are radiating outward to all parts of the axial lobe, into which its 

 fibres also seem to pass. The ventricle is obviously composed of 

 two portions, an outer and a median. The outer describes about a 

 semi-circle, extending from the supero-median portion to the 

 infero-lateral, separating a rather uniform thin mantle zone, which 

 is, however, thinnest laterally. The remaining median part of the 



