th a t there is no myodome. The list of fishes said, by one author or another, to be without a myodome
is thus large, and I have a ttempted to control it as far as my material and the literature a t m y disposal
will permit.
In Gadus aeglifinus, Brooks (’84) says th a t the prootic „unites below with its fellow of the
opposite side, and below this with the parasphenoid, th e three bones bounding a deep pit, which
is open anteriorly, and gives origin to the recti muscles of the o rbit“. This fish would thus seem
to possess a myodome, and as another one of th e Gadidae, Gadus merlangus, is easily obtained here,
I have examined it in this connection. In this fish there is, as in G. aeglifinus, a deep p it opening
into th e orbit and giving origin to certain of the recti muscles. The side walls of this p it are formed
by the ventral portions of th e prootics, those portions of those bones being capped with cartilage and
not meeting in th e middle line, a hypophysial fenestra, closed ventrally by the underlying p a ra sphenoid,
thus being left between them. The dorso-posterior wall, or roof of the p it is thick, and
is formed by the prootic bridge, th a t bridge being formed by the mesial processes of th e prootics
united by a thick median interspace of cartilage. The cerebral surface of this roof slopes postero-
ventrallv and forms a convex and triangular-shaped surface between the anterior ends of th e large
saccular grooves. The wide anterior edge of the roof is bevelled, th e bevelled surface sloping antero-
ventrally. The transverse edge th a t lies between this sloping, bevelled surface and th e posterior
portion of the roof of th e p it is continued dorsally, on either side, to form th e anterior boundary
of th e labyrinth recess. The bevelled surface gives a ttachment to the ventro-posterior edge of a thick
tough membrane th a t fills th e large orbital opening of th e brain case, a large pocket in this membrane,
immediately anterior to th e prootic bridge, lodging the pitu ita ry body. In th e anterior edge
of th e prootic there is, as in G. aeglifinus, a deep incisure for the exit of th e trigemino-facialis nerves,
and from this incisure a groove leads ventro-mesially into th e anterior end of th e myodomic p it. There
is no closed foramen w hatever in this p a rt of the prootic bone, all of th e nerves th a t pierce th e bone
in Scorpaena here passing across its anterior edge. There is also no internal carotid foramen between
th e prootic and parasphenoid, the internal carotid here passing inward .across th e anterior edge of
th e expanded, postorbital portion of th e parasphenoid; th a t edge of the parasphenoid lying slightly
anterior to th e anterior edge of th e ventral portion of the prootic. The anterior end of th e large
saccular groove is separated from th e bottom of the trigemino-facialis incisure by only a th in layer
of bone. There is no basisphenoid, b u t there is, as in Cottus, a considerable basisphenoid thickening
of th e membrane th a t closes the orbital opening of th e b rain case. Posterior to this thickened portion
of th a t membrane and p a rtly enclosed in it, in the region of th e membranous p itu ita ry fossa, is the
transverse commissure of th e pitu ita ry veins. There is thus here a normal myodome, b u t it has been
shortened b o th anteriorly and posteriorly. Posteriorly this shortening is due to a prootic constriction,
while anteriorly it is due to the absence of th e usual enclosing bones; for it is evident th a t the anterior
portions of th e bodies of th e prootics of Scorpaena, and the entire ascending processes of the p a ra sphenoid
of th a t fish, are absent in Gadus;
In a prepared skull th a t I have of Gadus morrhua, the conditions are all similar to those ju s t
described for Gadus merlangus, excepting th a t there is a median ossicle on th e cerebral surface of
th e cartilage of the prootic bridge, not found in G. merlangus. This ossicle is transverse in position
and extends from prootic to prootic along th e transverse edge th a t is continuous, on either side, with
th e anterior wall of th e corresponding labyrinth recess. I t is a s tout ossicle, of perichondrial origin,
and has never been described in any fish so far as I can find.
One further condition of the Gadoid skull needs to be mentioned. The hypophysial fenestra
is continued posteriorly, along the ventral surface of th e interprootic cartilage, by a relatively deep
groove which is prolonged posteriorly by two short recesses in th e anterior end of th e basioccipital,
th e two recesses being-separated by a thin, vertical, median wall of bone. Laterally, on either side,
this groove is in wide communication with a large and deep recess in the prootic. This recess extends
antero-dorsally in the bone, lying immediately mesial to the saccular groove and tapering toward
its dorso-anterior end, which end lies slightly postero-mesial to the trigemino-facialis incisure. The
bone th a t forms th e outer wall of the recess is thin, and seems to be of purely perichondrial origin.
In the specimens of Gadus merlangus th a t were particularly examined in this connection, and which
were all fresh specimens th a t had been slightly boiled, this recess was filled with loose and apparently
fa tty tissue: b u t in the skull th a t I have of Gadus morrhua, which had not been boiled, the reóess
lodged the spreading lateral portions of a membrane th a t covered th e ventral surfaces of the prootics
and th e interprootic cartilage, lying between those structures and the underlying parasphenoid. The
recess is certainly the homologue of th e prootic vacuity found in the prootic of the 45 mm Scorpaena,
as s tated when describing th a t fish.
In Uranoscopus scaber the interorbital wall is thick, and is deeply and widely excavated, on
its dorso-anterior edge, by th e large rostral depression. The central portion of th e floor of this
depression is formed by th e subcircular mesethmoid, the ventral surface of which bone rests directly
upon the underlying parasphenoid and, perhaps, also on the vomer; b u t the existence of this la tte r
contact was not established. The anterior portions of the side walls of the depression are formed
by th e deeply excavated ectethmoids, th e posterior halves of the same walls, and the hind wall,
being formed b y a specially developed flange of the frontal of either side. No alisphenoid is evident
as a separate bone, b u t it would seem to be represented in, or a t least to be replaced by, what appears
as an anterior process of th e sphenotic. With a ventral process of this alisphenoid p a rt of the
sphenotic, and also with an adjoining portion of the anterior edge of the prootic, the ascending process
of the parasphenoid is in contact. Posterior to this ventral process, the truncus maxillo-mandibularis
trigemini, undoubtedly accompanied by the buccalis lateralis, issues through a perforation of the
side wall of a well-developed trigemino-facialis chamber. The ramus ophthalmicus superficialis
issues from th e same chamber through a foramen th a t lies between th e suturating edges of the
parasphenoid and the ventral process of th e alisphenoid portion of the sphenotic. This ventral process
is, accordingly, a well developed parasphenoid leg of the alisphenoid process of the sphenotic.
Between the parasphenoid leg of th e alisphenoid process and the body of th a t process, dorsally,
th e parasphenoid posteriorly and ventrally, and th e rostral flange of the frontal and th e cartilage
covering the ventral p a rt of th a t flange, anteriorly, there is a large subcircular opening. This opening
gives exit to the olfactorius, opticus, oculomotorius and trochlearis nerves, and gives entrance to
certain of th e muscles of the eye, how many or which of them was not determined. The opening
is accordingly, in function, an olfactorio-opticus fenestra and an orbital opening of the myodome
combined. On th e internal surface of the prootic, a t a certain distance posterior to the hind edge
of this opening, there is a low transverse and nearly vertical flange which suturates in the middle
line with its fellow of the opposite side. That p a rt of the cranial cavity of the prepared skull th a t
lies anterior to this transverse vertical flange forms a recess in the cranial floor, b u t belongs properly
to the orbit and not to the cranial cavity. The canal for the internal carotid ^passes inward between
th e prootic and the hind edge of the ascending process of th e parasphenoid, and opens on the floor