310 EDWARD PHELPS ALLIS, JR. 
Diese indifferente Urdarmmasse schniirt sich zu Ende des Stadium F 
von den Gebilden der Mandibularregion vollstaéndig ab und stellt nun 
die Anlage der Priimandibularen Kopfhohle Balfour’s oder dasI. Somit 
van Wijhe’s dar. 
The protovertebrae are said by Froriep to extend the full 
length of the persisting notochord, and not to extend beyond 
that point; the whole animal being, at this stage, vertebral 
column. The prespinal, or head region is said to contain the 
matrix in which all the visceral arches and the mandibular and 
premandibular head cavities are developed. 
Katherine M. Parker, in the latest work I know of relating 
to this subject, also finds, in the Marsupiala, the notochordal 
tissue extending anteriorly beyond the end of the persisting 
notochord, for she says (’17, p. 24): 
The primitive relation of the tip of the notochord is one of continuity 
with the protochordal plate, and in Perameles continuity is retained 
between the chorda and the derivatives of the protochordal plate (pre- 
chordal plate and Seesel’s pocket). As a secondary condition, con- 
tinuity may be established between the chorda and the hypophysis. 
His, in a much earlier work, also came to a similar conclusion, 
for he says (’92, p. 348) that the notochord, in all early vertebrate 
embryos, ends anteriorly in a tapering point which les imme- 
diately posterior to a transverse basal ridge (Basilarleiste) of 
the brain which lies at the extreme anterior end of the ventral 
surface of the neural tube. This basal ridge is in contact, either 
with the dorsal end of Seesel’s pocket or with a strip of entoderm 
(Entodermstreife) which replaces that pocket, and His shows 
the tip of the notochord wedged in between his basal ridge and 
Seesel’s pocket in two different figures, one said to be a general 
vertebrate schema and the other to show an actual median 
sagittal section of the head of an embryo of Pristiurus 26-mm. 
in length. Seesel’s pocket lies at the dorsal edge of the oral 
plate, and is said to be not only topographically, but also genet- 
ically, an anterior continuation of the notochord (J. ¢., p. 350), 
the notochordal tissue thus extending to the level of the anterior 
end of the ventral surface of the neural tube. This primitive 
topographical relation of these four structures, the basal ridge, 
