FUNDAMENTAL PLAN OF VERTEBRATE BRAIN 469) 
On the other hand, no confirmation is afforded for the views of 
Schulte and Tilney. According to these authors, in the cat there 
exists in the neural tube a landmark of importance—the ‘tubercle 
of the floor.’ This marks the anterior end of the neural plate, thus 
forming the ventral lip of the neuropore and also the anterior 
end of the floor plate. Ventrally the tubercle of the floor is “in 
relation with the blind extremity of the foregut (while) the stomo- 
daeum approaches but hardly reaches it in front” (p. 339). In 
later stages “it forms a transverse ridge intervening between the 
mammillary and infundibular regions.” The optic vesicles at 
an early stage form the cephalic extremity of the neuraxis and 
between these there exists an ‘optic sulcus’ crossing the mid- 
plane anterior to the tubercle and partially interrupted (caudally) 
by it. The optic vesicles during growth, as they interpret, 
decrease in size contributing the infundibular region caudally 
and the anlages of the thalamencephalon and telencephalon 
anteriorly (cephalically). The line of closure of the neuropore 
they thus consider very extensive, including lamina terminalis, 
optic chiasma, and infundibulum as well. 
As stated in my earlier paper, the critical point is the interpre- 
tation of the ‘tubercle of the floor,’ and it was there commented 
that the figures offered by them in illustration ‘‘neither conclu- 
sively show that it corresponds to the anterior end of the neural 
plate nor that it marks the anterior boundary of the mammillary 
recess.”” As to the first point above it may be urged that their 
figure 1 of plate 27 (cat of four somites in which the neural folds 
have not yet fused) shows, on the contrary, that there intervenes 
between the ‘tuberele of the floor’ and the anterior end of the 
brain plate the primitive optic furrow (their ‘optic sulcus’) and 
a terminal ridge in which, in the light of Johnston’s work and 
my own observations, I should be inclined to see a chiasmatic 
ridge. Their figure (1 of plate 27) might well be compared with 
figure 10 (9 and 11) in this paper of the neural plate of the shark. 
Flatten out the neural plate as it is shown in their model in the 
cat and the equivalence would be quite striking. 
The shark, however, possesses no well-defined ‘tubercle of the 
floor.’ The slight elevation, which from their description of the 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 34, NO. 5 
