THE TELENCEPHALON IN CYCLOSTOMES 363 
fundamental in vertebrates. A further examination of the pallial 
commissures in reptiles and mammals with reference to this is in 
progress (see 710 ¢). 
Anterior commissure 
This commissure is rather small in cyclostomes. It lies in the 
lamina terminalis in front of the preoptic recess as in all verte- 
brates. Its constitution is not at all clearly known. Its fibers 
probably come from the basal (lateral) olfactory area and the 
so-called ‘striatum.’ 
The ‘striatum’ 
The region to which the naine striatum has been applied includes 
the supraoptic portion of the telencephalon medium and an 
adjacent part of the hemisphere (figs. 5, 6, 22). It is clear that 
this corresponds roughly to the striatum of other fishes. The 
writer has shown (’02 a, p. 41) that the descending fibers from the 
‘striatum’ go to the thalamus and not to the hypothalamus. 
From this region fibers pass through the anterior pallial commis- 
sure, as noted above. These facts suggest that the striatal region 
corresponds to or contains the equivalent of the somatic area of 
selachians. Any decision on this point must await further study. 
Mode of evagination of hemispheres. Zona limitans 
The cyclostomes taken in comparison with higher forms -give 
clear evidence of the principle announced by the writer (710 ¢, 
"11 a) that the hemispheres are lateral evaginations of the telen- 
cephalon which have gradually involved the formatio bulbaris, 
the lobus olfactorius and the pallium in the order named. The 
comparison of the cyclostomes with selachians and amphibians 
with reference to the mode by which the more fully evaginated 
brains have come to have their present form, is very important 
for the interpretation of these higher brains. 
If attention be given to the models shown in figures 5, 6 and 7, 
it will be seen that the further evagination of the hemisphere 
involves the turning out of the primordium hippocampi and the 
