The mesial process of the prootic of Scorpaena has, as it has in Scomber, anterior and posterior
portions, the pituitary opening of the brain case lying between the two portions. Immediately
posterior to the pituitary opening, a small process of the postpituitary portion of the main process,
projecting mesially, suturates with a corresponding process of the opposite side. Posterior to this
little suturating process the mesial edge of the main process is connected by synchondrosis, by a
median interspace of cartilage, with its fellow of the opposite side. On its dorsal surface, this interspace
of cartilage is considerably wider than on its ventral surface, a thin lamina of the ventral layers
of the process of the prootic projecting mesially, nearly to the middle line. Posteriorly, the interspace
of cartilage is continuous, along the hind edge of the prootic, with the cartilage th a t caps the ventral
edge of the bone, the hind edge of these united bands of cartilage bounding the anterior end of the
basioccipital and connecting that bone, by synchondrosis, with the prootic. The anterior boundary
of the pituitary opening is formed by a small sharp process of the prepituitary portion of the mesial
process of the prootic. This little process lies, as already stated, against the ventral surface of the
hind edge of the basisphenoid, and usually extends to the middle line of the skull, where it suturates
with its fellow of the opposite side, thus completely cutting off the basisphenoid from all bounding
participation in the pituitary opening. Antero-dorsal to this little pituitary process of the prepituitary
portion of the entire process, the process suturates with the basisphenoid and the alisphenoid,
as in Scomber.
The pituitary opening of the brain case of Scorpaena is closed, in the recent state, by membrane,
this membrane being slightly concave on its dorsal surface, and slightly convex on its ventral
surface. A slight depression is thus formed in the floor of the cranial cavity, this depression underlying
the pituitary body and being the pituitary fossa. The pituitary opening of the brain case of
the adult Scorpaena is, accordingly, the functional equivalent of the so-called pituitary fossa (Swinner-
ton), or pituitary space (Parker) of teleostean embryos: and an opening, similar to this one in
Scorpaena, must certainly be found, at some stage, in all fishes the adults of which possess a basisphenoid
bone. But the opening, though shown in certain figures of median sections of the teleostean
skull, has seldom been particularly described. In Scomber I fully described it, using the word opening
in place of fenestra so as to avoid, as much as possible, any suggestion of an homology.
On the internal surface of the prootic, near the sutural comer between this bone, the alisphenoid
and the basisphenoid, is the internal opening of the foramen for the nervus oculomotorius. Posterior
and slightly lateral to the pituitary opening the mesial process of the bone is perforated by the
foramen for the nervus abducens, that nerve passing from the cranial cavity directly into the myo-
dome. Lateral to these two foramina are the internal openings of the trigeminus, facialis, profundus
and palatinus foramina; the first three foramina piercing the body of the bone to enter the trigemino-
facialis chamber, while the palatinus foramen perforates the base of the mesial process of the bone
and so enters the myodome. All four of these foramina lie in what is, in some specimens, a simple
depression, but in others a marked recess on the internal surface of the bone. The hind wall of this
recess looks postero-laterally and forms part of the anterior wall of the labyrinth recess, th a t wall
being represented, both dorsal and ventral to the pocket, by a low ridge of bone; the dorsal ridge
being continuous dorsally with the flange of bone th a t separates the two recesses on the internal
surface of the sphenotic, and the ventral ridge vanishing along the mesial boundary of the saccular
groove. The roof of the recess is formed by a nearly horizontal, shelf-like web of bone which extends
across the angle that lies between the anterior wall of the labyrinth recess and the body of the prootic
anterior to th a t wall. A much smaller but similar web of bone may separate the recess into dorsal
and ventral portions, the facialis and palatinus foramina leading, in such cases, from the ventral
portion of the recess, and the trigeminus and profundus foramina from its dorsal portion. The recess
lodges the profundus ganglion and also the lateralis and communis portions of the trigemino-facialis
ganglionic complex. The recess can accordingly be called the trigemino-facialis recess, although,
as already stated, geniculate recess might be a more proper designation.
The canal for the ramus palatinus facialis thus perforates, in Scorpaena, the base of the mesial
process of th e prootic and does not enter the trigemino-facialis chamber in any p a rt of its course;
and this is the condition found also in th e Characinidae (Sagemehl, ’84 b, p. 65) and Cyprinidae
(Sagemehl, ’91, p. 558). In Scomber, on the contrary, th e nerve first enters the trigemino-facialis
chamber and then pierces the prootic to enter the myodome (Allis’03). In Trigla Lepidotrigla and
Dactylopterus, as will be later shown, the nerve also first enters th e trigemino-facialis chamber, b u t
instead of then piercing the prootic by a separate canal, as in Scomber, it simply issues by the trigeminus
opening of th e chamber and so enters the orbit. In Menidia, the nerve is said by Herrick
(’99, p. 176) not to enter the myodome (sub-cranial canal), butto run „along the outer side of the
canal, n o t the inner” ; thus apparently being either as in Scomber, or as in Trigla Lepidotrigla and
Dactylopterus.
Immediately posterior to the trigemino-facialis recess; the labyrinth recess begins, and in
th a t recess, on the internal surface of the prootic and immediately dorso-postero-lateral to the
trigemino-facialis recess, there are two adjoining depressions, the anterior one lodging the ampulla
of the anterior semicircular canal, and the posterior one the ampulla of the external canal. Ventro-
mesial to these depressions, and immediately posterior to the ventral portion of the trigemino-
facialis recess, a large and deep longitudinal groove begins, and, extending backward to the hind
end of the prootic, immediately dorsal to the base of the postpituitary portion of the mesial process
of the bone, forms the anterior portion of the saccular groove. The bottom of this groove is thin,
and this part of the prootic forms, on the outer surface of the skull, the anterior part of the bulla acustica.
The conditions in the prootic region of 45 mm specimens, examined in serial sections, must
now be considered. In these specimens, the basisphenoid bone is just beginning to develop, and lies
immediately posterior and ventral to the posteriorly directed dorsal end of th e basisphenoid cartilage.
Excepting only this little bone and cartilage, the floor of th e cranial cavity is, a t this age, wholly
membranous from its anterior end back to the abducens foramina. Immediately posterior to the
abducens foramina, the cranial floor is formed by a horizontal bridge of cartilage which corresponds
exactly, in ex ten t and position, to the bony bridge formed by the united mesial processes of the prootics
of the ad u lt Amia. B ut th e saccus vasculosus lies, both in these 45 mm specimens and also in the
a d u lt Scorpaena, on the dorsal surface of this prootic bridge, while in Amia it lies (Allis, ’97 a, pp. 494
und 505) ventral to th a t bridge. As th e bridges in these two fishes are unquestionably homologous,
this difference in the position of the saccus, if the sacci also are homologous, must be caused by its
being, in Scorpaena, pulled out from beneath, and lifted up above th e bridge, by the greatly
developed hypoaria; the saccus thus being pulled out of the myodome and so losing all relation to
th a t canal.
Those parts of the mesial processes of the prootics of the adult Scorpaena th a t lie anterior
to the abducens foramina are thus not preformed in cartilage, and must accordingly be developed
wholly in membrane, as I was led to conclude, in an earlier work (’97), th a t they m ust be in all teleosts.