258 EDWARD PHELPS ALLIS, JR. 
(1. c., fig. 8345, p. 669), lying ventral to the musculi recti interni, 
and it is furthermore said that it gives attachment on its dorsal 
surface to the metachiasmatic (posterior) portion of the inter- 
orbital septum. The posterior portion of the interorbital sep- 
tum here referred to is evidently the median vertical myodomic 
membrane of my account, the membrane that closes the fenes- 
tra hypophyseos then being represented in the layer of skeletog- 
enous tissue forming the floor of what I have called the sub- 
pituitary portion of the ventral compartment of the myodome. 
The roof of the anterior section of the myodome, as thus de- 
cribed by Gaupp, is said by him to be formed by the mem- 
branous floor of the cranial cavity, and its side walls by the 
ventral portions of the cartilaginous side walls of the cranium, 
which are said to here extend between the otic capsules and the 
trabeculae. The eye muscles are said to have forced the brain 
upward from the basis cranii, the hypophysis being carried 
with it and so lifted out of the fenestra hypophyseos. 
The middle section of the myodome is said by Gaupp to lie, 
in part, in the labyrinth region and, in part, in the extreme pos- 
terior (hintersten) portion of the orbitotemporal region. Its 
floor is said to be formed by the anterior prolongations of the 
parachordals (vordere Parachordalia) which have been forced 
ventrally by the pressure of the musculi recti externi, exactly 
as Swinnerton had previously said was the case in Gasterosteus. 
Gaupp, however, shows the hind ends of the trabeculae—the 
parts bounding the fenestra hypophyseos—forced ventrally 
to the same extent as the parachordals. Because of its rela- 
tions to the anterior parachordals, this middle section of the 
myodome is said to lie between the primordial basis cranii and 
the brain, and hence to form a part of the primordial cranial 
cavity. Its side walls are described as formed, on either side, 
by two basicapsular commissures, which extend from the otic 
capsule of their side to the anterior prolongation of the related 
parachordal, and lie, one between the nervi trigeminus and 
facialis, and the other between the latter nerve and the otic 
capsule. Its roof is formed by the membranous floor of the 
cavum cerebrale cranii, this membrane arising, on either side, 
