61 
In general, then, it seems proper to regard the cerebral hemi- 
spheres as a product of a dorso-lateral pouch from the thalamus car- 
rying with it the commissural systems (dorsal and ventral) belong- 
ing to what may be called the praethalamic segment or neuromere. 
The hippocampal system may be regarded as representing a part of 
the dorsal commissure, the callosum a part of the ventral and perhaps 
also a part of the dorsal, while the anterior commissure is decidedly 
ventral. It is interesting to note that the pes olfactorii is connected 
with the ventral system and the pero with the dorsal via hippo- 
campus. 
Our conclusions may therefore be briefly summarized as follows: 
1) Fishes have a distinct corpus callosum separate from, and 
on the opposite side of the ventricle from the praecommissura. 
2) Fishes have a distinct fornix and hippocampal commissure. 
3) A well-formed fornix body is present in Teleosts with the 
usual fibre connections. 
4) The hippocampus of fishes is a distinct lobe of the axial 
portion of the cerebrum. 
5) There are distinct radices mesalis and lateralis, the former 
crossing in the anterior commissure and the latter passing directly 
to the hippocampal lobes. 
6) The axial lobe in fishes is composed not only of the elements 
proper to the corpus striatum but also contains rudiments of the 
sensory and motor niduli of the cortex. 
7) The two types of cells are sharply differentiated. 
