MYODOME AND TRIGEMINO-FACIALIS CHAMBER oul 
the tip of the notochord, Seesel’s pocket, and the dorsal edge 
of the oral plate, is said to be subject to marked changes in 
later stages and in different vertebrates, Seesel’s pocket shifting 
either anteriorly or ventrally (rachenwirts) relatively to the 
basal ridge. In the latter case an ectodermal fold is formed 
between it and the basal ridge, and becomes the hypophysial 
invagination (Rathke’s pocket), which extends posteriorly be- 
yond the basal ridge, forcing the tip of the notochord away 
from the ventral surface of the brain, and even forcing it upward 
into the plica encephali ventralis. The relations of the brain 
to the notochord, in the adult vertebrate, are accordingly said 
by His not always to be the primitive ones, and he (l.c., p. 358) 
considers only those parts of the brain of the adult to be pre- 
chordal which lie anterior to the basal ridge, and which therefore 
formed primarily a part of the anterior surface of the neural tube. 
Those parts are said by him to be the regions of the recessus infun- 
dibuli, the chiasma opticum, the recessus opticus, the lamina ter- 
minalis, and the olfactory lobes. The saccus vasculosus lies 
posterior to the basal ridge and belongs morphologically, as well as 
actually, to the ventral surface of the brain, the line between the 
morphologically ventral and anterior surfaces of the brain thus 
lying between the saccus and the recessus infundibuli. 
There is thus reason to believe that the notochord extended 
primarily to the level of the anterior end of the primitive gut, 
and that, accordingly, the epichordal and hypochordal bands 
of skeletogenous material, developed in relation to it, had a 
similar extent. The polar and trabecular cartilages must then 
be developed from some part of these anterior extensions of 
these bands, and the polar cartilages quite certainly, as already 
stated, from the hypochordal bands alone. The trabeculae, 
in crania of the platybasic type, would seem to be developed 
from both these bands of tissue. In crania of the tropibasic 
type the two bands seem to have been forced apart, by pressure 
of the eyeballs, the epichordal bands lying at the top of the 
interorbital septum and the hypochordal bands at the bottom 
of that septum. 
It is furthermore to be noted that the trabeculae do not lie 
