MYODOME AND TRIGEMINO-FACIALIS CHAMBER 245 
zontal membrane, and it is traversed by the internal carotid 
arteries. ‘The membranous roof of the subpituitary portion 
of the myodome extends forward from the horizontal proc- 
esses of the prootics to the hind edge of the horizontal plate 
of the basisphenoid. The conditions in this fish are thus wholly 
normal. 
Starks (’05) says that the dorsal end of the basisphenoid 
(dichost, Starks) of this fish is ‘free,’ and he suggests that this 
should be examined in connection with a ‘myodome septum’, 
formed of connective tissues, said by him to be found in this 
region and to be continued forward as the interorbital septum. 
Just what this myodome septum is is not clear, but it would seem 
to be the membranous roof of the myodome. Starks further 
says that “the dichost (=basisphenoid of Huxley) is always 
absent when the myodome is.’’ No particular cases are cited, 
but it is evidently assumed that there is no myodome whenever 
a prootic bridge (shelf) is not found in the prepared skeleton 
of the cranium. ‘This is incorrect, and the statement should 
probably be that there is no basisphenoid whenever the roof 
of the myodome is wholly of membrane. Whether or not this 
statement is true, even in this form, I do not know, my material 
being too limited to permit me to form an opinion. 
GASTEROSTEUS ACULEATUS 
The early stages of the development of the myodome in Gas- 
terosteus aculeatus are quite fully described, and the myodome 
of the adult briefly described by Swinnerton (’02). The trabec- 
ula and parachordal of either side are said by him to be, when 
first formed, wholly independent cartilages, and their adjoin- 
ing ends are shown in the figures lying approximatively in the 
tranverse plane of the tip of the notochord. The posterior 
halves of the trabeculae are said to enclose the infundibulum 
and the pituitary body, and the infundibulum is shown lying 
posterior to the pituitary body and reaching to the tip of the 
notochord. ‘The trabeculae and parachordals soon fuse with 
each other, and there is then a marked anterior growth of the 
parachordals which carries the trabeculae forward considerably 
