MYODOME AND TRIGEMINO-FACIALIS CHAMBER 239 
eranil, the space between the two being filled with dense con- 
nective tissue which is bounded laterally at its dorsal edges 
by little projecting flanges of perichondrial bone developed 
in relation to the cartilage of the basis cranil. The hind end 
of the myodome lies in this tissue, and lodges the hind ends 
of the recti externi. Proceeding anteriorly from this point, 
the cartilaginous roof of the myodome soon vanishes and is re- 
placed by a thick layer of fibrous tissue. Cartilage is, however, 
now found in the ventral portion of each lateral wall of the myo- 
domic cavity, this cartilage being enclosed between projecting 
flanges of the parasphenoid, one of these flanges lying along 
the external surface of the cartilage and the other along its 
internal surface. The internal flange lies in the fibrous tissue 
that lines the myodome, and is certainly developed in relation 
to it. 
‘The internal carotid artery traverses its foramen at the hind 
edge of the ascending process of the parasphenoid, and then 
immediately enters and runs upward in the median vertical my- 
domic membrane, its course and distribution there being as 
in Sygnathus. The recti interni, superiores and inferiores 
have their origins anterior to this ascending column of the artery, 
close together, from the dorsal surface of the parasphenoid. 
The ventral compartment of the myodome is thus here wholly 
prespinal in position, for the foramen for the internal carotid 
artery lies in the plane of the pituitary opening of the brain 
case. The relations of these two openings to each other varies 
considerably in different fishes, the foramen for the artery lying 
markedly anterior to the pituitary opening in Scorpaena, but 
posterior to that opening in Scomber. 
CATOSTOMUS 
In Catostomus teres, Sagemehl (’91) describes a myodome 
that is everywhere closed ventrally by the parasphenoid, is 
bounded dorsally by the horizontal processes of the prootics, 
and apparently extends posteriorly slightly into the basioccipital. 
The basioccipital has a large pharyngeal process, perforated 
by a short canal which encloses the dorsal aorta, and Sagemehl 
