cavity, forms tlie dorsal portion of the anterior wall of the labyrinth recess. The posterior recess on
th e internal surface of th e bone thus forms p a rt of the labyrinth recess, b u t it lodges, in the adult,
no p a rt of the membranous ear, lying wholly dorso-anterior to the curved anterior edge of the anterior
semicircular canal. The anterior recess forms th e latero-postero-dorsal corner of th a t p a rt of the
cranial cavity th a t lies between th e labyrinth and fore-brain recesses, and would accordingly seem to
be a mid-brain recess.
Ridewood says (’04a, p. 56) th a t th e sphenotic is found distinct from th e postfrontal in b u t
a few fishes. I, on th e contrary, find these two bones almost invariably distinct and separate. Ride-
wood further says th a t th e sphenotic is an endosteal ossification „ se t up in sympathy w ith“ th a t
ossification in th e dermal tissues th a t gives origin to the postfrontal; and he accordingly considers
the name sphenotic redundant. This relation of these two bones to each other I do not consider as
established.
In the Barbidae, according to Sagemehl (’91, p. 573), th e anterior semicircular canal may
be enclosed in a canal in the sphenotic. This semicircular canal thus has this relation to th e sphenotic
in th e Barbidae, while in Elops, as I have already stated, it traverses a canal in th e alisphenoid.
Swinnerton, in his descriptions of Gasterosteus, uses th e te rm „postorbital process“ in a
manner th a t might be confusing. On p. 532 of his work on th a t fish he says „ th e postorbital process,
which in o ther teleosts forms p a rt of the alisphenoid, remains unossified“ . The process of Gasterosteus
here referred to is an outgrowth of the auditory capsule which projects forward in th e dorsal portion
of the hind end of the orbit, and is accordingly more properly an orbital or supraorbital process, th an
a postorbital one; and it is the lateral corner of its base, alone, th a t is th e postorbital process, as th a t
term is commonly used, and it ossifies in Gasterosteus, as in other fishes, as th e sphenotic.
B A S I S P H E N O I D .
The basisphenoid is, as usual, T-shaped, th e ventral end of its pedicle abutting against a
median nodule of cartilage th a t lies on th e dorsal surface of th e parasphenoid. The anterior edge
of the pedicle is strongly curved, running a t first forward and downward, or sometimes even directly
forward, and then curving downward, and downward and backward. The dorsal portion of the
pedicle is usually expanded into a relatively large median plate, and this p a rt of th e pedicle is often
independent of th e ventral portion, touching and being bound to th a t portion, b u t n o t being continuous
with it; th e pedicle of th e bone thus being in two, and sometimes even in three separate
pieces. The pedicle, as usual, separates th e anterior opening of the myodome into two parts, and
its anterior edge gives insertion to th e hind edge of th e ventral portion of the membranous posterior
portion of th e interorbital septum.
The body of th e basisphenoid is almost flat, and occupies a nearly horizontal, transverse
position. Its posterior edge, on either side, is overlapped ventrally by, and lies against th e dorsal
surface of a small process of the prepituitary portion of the mesial process of the prootic, these small
prepituitary processes of th e prooties of opposite sides meeting in th e middle line and thus shutting
off the basisphenoid from th e anterior edge of th e p itu ita ry opening of th e brain case. In Scomber
(Allis, ’03), th e basisphenoid forms p a rt of th e anterior edge of th e la tte r opening. In Amia the
anterior edge of th e opening is formed by . a transverse bolster of cartilage, th e actual anterior edge
of th e p itu ita ry fossa being, however, formed of membrane only.
In 45 mm Scorpaenas the basisphenoid is ju s t beginning to form, appearing as a thin g u tte rshaped
lamina of bone in th e midst of the dense fibrous tissues which form the floor of this p a rt of
the cranial cavity and th e roof of th e anterior portion of the myodome. Immediately anterior to
this little bone there is a small median nodule of cartilage which lies between th e extreme hind ends
of th e recti inferior muscles, imbedded in the anterior end of a median vertical band of tough fibrous
tissue which gives origin to those muscles and will be further described when describing th e myodome.
This little nodule of cartilage is connected, antero-ventrally, by a delicate median line of cartilage,
with the nodule of cartilage on which, in th e adult, the pedicle of th e basisphenoid rests, and this
la tte r nodule is connected anteriorly, also by a delicate line of cartilage, with th e cartilage of the
interorbital septum. The pedicular line of cartilage together with th e dorsal nodule thus form a
basisphenoid cartilage which must certainly be the somewhat reduced homologue of th e transverse
prepituitary bolster of Amia. The basisphenoid bone of th e adult Scorpaena is thus probably a peri-
chondrial ossification related to this basisphenoid cartilage of the young Scorpaena, b u t it certainly
extends beyond th e cartilage, into the adjacent tissues, these tissues representing, in p a rt a t least,
pa rts of the primary membranous cranium th a t have n o t chondrified.
PROOTIC.
The prootic (petrosal) has lateral and orbital surfaces, the former forming a considerable
p a rt of the side wall of th e brain case, and th e la tte r a small p a rt of th e hind wall of the orbit.
The bone is bounded dorsally by th e sphenotic and pterotic, antero-mesially by th e alisphenoid, and
posteriorly by th e exoccipital and basioccipital; with all of which bones it is either in contact or in
synchondrosis. Its hind edge is, in part, slightly overlapped externally by the anterior edge of the
opisthotic. Its ventral edge is overlapped externally by the lateral edge of the parasphenoid. The
prepituitary portion of its mesial process suturates with th e basisphenoid and alisphenoid.
The angle separating th e lateral and orbital surface of th e bone forms the ventral portion
of th e postorbital process of the skull, and on the dorsal end of this p a rt of th e bone lies the ventral
portion of th e anterior articular facet for th e hyomandibular. The hind edge of this facet is raised
to form a ridge which ends, a t th e dorsal edge of the bone, as a pronounced process, and this process,
as already stated, gives origin to certain of the levator muscles of the branchial arches. The process
lies between th e articular facets for th e anterior and posterior heads of the hyomandibular, and
abuts against th e inners urface of th e hyomandibular between its two articular heads, th e hyomandibular
being often here perforated by a circular opening due doubtless to wear. Immediately posterior
to the ridge and process, there is, on the lateral surface of th e bone, a marked depression or pit,
which, as already described, also gives origin and lodgment to certain of the levator muscles of the
branchial arches. In one specimen the p it was unusually deep, and a t the bottom of it there was a
smaller pit, which gave insertion to one of th e levator muscles, doubtless the internus anterior.
This smaller p it in this one specimen extended forward into the postorbital process, and perforating
th e prootic, near its edge, was bounded mesially by th e sphenotic, a th in plate only of th a t bone
separating it from the cerebral recess for the anterior semicircular canal.
The angle th a t separates the lateral and orbital surfaces of the prootic is traversed by a
canal which is th e homologue of th e more extensive trigemino-facialis chamber of my descriptions
of Scomber. The nervus facialis issues from th e posterior opening of this chamber, and th e trige