220 EDWARD PHELPS ALLIS, JR. 
form a matrix, in relation to which the body and ascending 
processes of the parasphenoid are developed, and from” here 
forward for a certain distance teeth are found developed in re- 
lation to this bone. The roof of the cavity forms a membrane 
which extends transversely from the ventral end of one per- 
sisting cartilaginous side wall of the myodome to the other, this 
membrane being horizontal in position in its posterior portion, 
but arching upward anteriorly to such an extent that, in the 
subpituitary region, its summit reaches nearly to the middle 
of the height of the entire myodomic cavity. The parasphenoid 
has in this region been inclining quite rapidly ventrally, this, 
and the arching upward of the membrane, leaving a space be- 
tween the two and separating the myodomic cavity into dor- 
sal and ventral compartments. The ventral compartment, lim- 
ited to the region of the ascending processes of the parasphe- 
noid, is bounded both laterally and ventrally by that bone. 
The dorsal portion of the dorsal compartment is bounded later- 
ally by the ventral processes of the prootic bone, its ventral por- 
tion being bounded in part by the ventral portions of those proc- 
esses, overlapped externally by the ascending processes of the 
parasphenoid, and in part by the latter processes only. The 
dorsal compartment still lodges the recti externi, the ventral 
compartment lodging the hind ends of the recti interni and the 
internal carotid arteries, the two being separated by a delicate 
line of tissue (fig. 3). 
Slightly posterior to the internal carotid foramina in the para- 
sphenoid, the roof of the myodome, formed by the horizontal 
processes of the prootics, is traversed at each lateral edge by 
both the nervus abducens and the ramus palatinus facialis, appa- 
rently through a single foramen (fig. 4). The abducens goes 
directly to the muculus rectus externus. The palatinus facialis 
runs ventrally along the internal surface of the side wall of the 
dorsal compartment of the myodome, passes through a notch 
in the anterior edge of the ventral end of the prootic portion of 
that wall, which is wholly of cartilage, and then, continuing 
ventrally between that cartilaginous wall and the ascending 
process of the parasphenoid, enters that portion of the ventral 
