FUNDAMENTAL PLAN OF VERTEBRATE BRAIN 473 
infundibular fold are continuous with one another. As the 
brain expands the primitive infundibulum becomes extended 
cephalo-caudally and loses its direct and primary communica- 
tion with the optic vesicles (figs. 30, 31, 32). 
A comparison of these figures (figs. 27 to 30) will also sub- 
stantiate the important point that the primitive infundibulum 
(primitive optic furrow) is within the territory of the brain plate. 
The preoptic recess appears later (fig. 32). From the relations, 
which were well ascertained by Johnston (’09), it is apparent 
that the optic chiasma, although it appears only subsequently, 
marks the anterior boundary of the optic furrow and the anterior 
limit of the brain plate medially. 
From the examination of the relations in the chick, as in the 
case of the shark, the interpretations of Schulte and Tilney lack 
substantiation. In the chick, as in the mammal (e.g., cat, 
Schulte and Tilney), the early formation of the neural folds dis- 
guise relations that are clearer in the shark due to the greater 
expansion of the brain plate (cf. figs. 9, 10, 11) before the neural 
folds rise up. Were one to ‘open out’ the neural folds in, say, the 
four- to six-somite chick as in the four-somite cat of Schulte and 
Tilney, the morphological identity would be quite striking. 
The prominences seen in the median plane reconstructions of 
the chick (figs. 27 to 30) correspond closely to Schulte and Tilney’s 
tubercle of the floor. Whether the second (slight) furrow cor- 
responds with the future mammillary recess was not determined. 
I am inclined to regard these prominences—as indeed the fur-_ 
rows—as but expressions of the growth mechanics of the region 
and caused mainly by a crowding forward. 
2. The sutura terminalis (anterior) 
In the His conception of the brain as a tube a separate anterior 
closing sutura, sutura frontalis (terminalis, anterior), ‘frontale 
Endnaht,’ would have a distinct morphologic significance. If, 
however, it is recognized that the brain is developed from a plate 
folded together while it grows, such a theoretical significance 
would not attach to this portion of the secondary line of closure. 
As is well known, the dorsal suture is first formed somewhere 
