end of th a t th in median ridge-like portion of the basioccipital th a t separates th e saccular grooves,
and th a t supports, on its dorsal edge, th e mesial edges of th e mesial processes of th e exoccipitals.
There, th e mid-longitudinal line of the floor changes abruptly in level, the immediately posterior
portion lying a t a slightly higher level, in a nearly horizontal position, on th e dorsal surface of the
platform formed b y th e united mesial processes of th e exoccipitals. Posterior to this platform the
floor slopes into th e cavum sinus imparis, posterior to which there only remains th e narrow edge
of bone th a t forms th e ventral bounding edge of th e foramen magnum.
The th in raised platform formed by th e united mesial processes of the exoccipitals lies on
a level with the p itu ita ry opening of th e brain case, and under this platform, on either side, lies the
posterior portion of th e large saccular groove. Anterior to the exoccipital platform the saccular
grooves diverge, on either side, th e central portion of th e floor of th e cavity widening gradually
from a th in median line a t th e edge of the platform, to its widest portion, immediately anterior to
th e anterior ends of the saccular grooves. A t either lateral corner of this widest portion lies th e tri-
gemino-facialis recess, in which are the facialis, trigeminus, palatinus and profundus foramina, and
approximately between these recesses, in th e m edian line, is th e pitu ita ry opening of the brain case.
Between th e recess of either side and the anterior end of th e corresponding saccular groove, there
is a th in bony partition which forms th e ventro-mesial portion of th e anterior wall of th e large
labyrinth recess, th a t wall extending from there antero-dorso-laterally across th e prootic and
sphenotic. In th e lateral wall of th e labyrinth recess there are four small recesses, all related to the
semicircular canals, and all separated from each other, and more or less surrounded by important
cartilaginous remnants of th e chondrocranium. In th e bottom of th e anterior one of these four
recesses there are two depressions, separated b y a low rounded ridge. The ventro-mesial depression
lies in th e prootic and lodges th e ampulla of th e anterior semicircular canal, th e dorso-lateral
depression lying in th e sphenotic and being related to the rounded antero-dorsal corner of the
anterior semicircular canal, th a t canal lying wholly exposed in the cranial cavity. The next posterior
one of the four recesses also has two portions, one of which lies in th e prootic and lodges th e ampulla
of th e external semicircular canal, while the other portion leads into th e pterotic and encloses the
lateral portion of th e same canal. The postero-ventral recess has three portions, a little pit-like
depression in th e exoccipital, to lodge the ampulla of th e posterior semicircular canal, and the
cerebral openings of two canals which enclose respectively th e hind end of th e external canal and
th e ventral end of th e posterior canal. The dorso-posterior recess lies in th e epiotic, is large, and
has, in its ventro-posterior wall, a small opening which leads into the canal for th e posterior semicircular
canal, th a t canal traversing th e epiotic. In Amia, th e hind wall of th e labyrinth recess is
formed b y an important cartilaginous ridge, membranous in its middle portion, which projects antero-
mesially from the lateral cranial wall and separates th e labyrinth recess from an important posterior
portion of th e cranial cavity which I described (’97, p. 703) as th e postauditory or occipital chamber.
If th e membranous ear of Amia, and in particular th e sacculus, were to be greatly developed, the
labyrinth recess would have to be correspondingly enlarged, and this would necessarily push the
posterior wall of th e recess backward and mesially, th e vagus foramen remaining always posterior
to th e wall. As th e saccular recess was thus pushed backward it would split the dorsal edge of the
basioccipital and th e ventral edge of th e exoccipital each into two parts, one of these parts forming
the outer and th e other th e inner wall of th e recess, and so give rise to a saccular groove on the
dorsal surface of the former bone and to a mesial process, roofing th a t groove, on the internal surface
of th e la tte r bone. The mesial process of the exoccipital of Scorpaena is, accordingly, a definite
p a rt of the cranial wall and n o t simply an ossification of the dura mater, as Sagemehl considered
i t to be (*84 b, p; 85). That p a rt of th e process th a t, in th e Characinidae and Cyprinidae, is said by
Sagemehl to roof th e cavum sinus imparis may however be such an ossification; for this cavum lies
in th e cranial cavity itself, and not in th e walls of th a t cavity, as th e saccular recess does. The true
internal, or cerebral surface of these two occipital bones of Scorpaena is accordingly formed by the
mesial processes of the exoccipitals and by th a t small portion of the dorsal surface of the basioccipital
th a t lies between those processes. The nervus glossopharyngeus first perforates the mesial, membranous
wall of th e labyrinth recess and then the outer, bony wall of th e recess, as in Amia, traversing,
in its course, a space th a t is hollowed out of th e cranial wall to reoeive th e ear and th e ganglion of
th e nervus acusticus.
The anterior portion of th e cranial cavity of Scorpaena is enclosed between the alisphenoids
and th e ventral flange-like processes of th e frontals, and does not, in th e adult, lodge any portion
of the brain, th e brain being small, relatively to the cranial cavity, and its anterior end reaching,
approximately, only to th e level of the hind edge of the basisphenoid. This p a rt of the cranial cavity,
in the dried skull, opens ventrally, by a relatively long and narrow median opening, into the hind
end of the orbit, and this opening, bounded posteriorly by th e basisphenoid, is the orbital opening
of the brain case. In the recent state it is closed by th e flaring dorso-posterior edge of the membranous
posterior portion of the interorbital septum. Posterior to the hind edge of the basisphenoid,
and extending approximately to th e hind edge of th e prooties, there is, in th e recent state, when
th e brain is removed, a large, nearly round, pit-like depression, formed in th e fa tty and connective
tissues th a t cover th e floor of th e cavity. This depression lodges th e hypoaria, and has, near the
anterior edge of its floor, a small saucer-like depression which lodges th e pitu ita ry body and overlies
th e pitu ita ry opening of the brain case.
2. I N F R A O R B I T A L C H A I N O F B O N E S .
The infraorbital bones are the three so-called suborbital bones of current descriptions, and
a small postorbital bone, which la tte r bone has, so far as I can find, never been described.
The three so-called suborbital bones are, as is well known, firmly bound together to form
a single rigid piece which extends backward across the cheek and abuts against and is firmly bound
to the outer surface of the preopercular. The anterior one of these three bones, which I shall call
th e lachrymal, is an irregular five or six rayed bone, and is called by both Gunther (’60) and Boulenger
(’04) the preorbital. The several rays of this bojie are of varying and unequal proportions, and their
bases are connected, excepting between the dorsal and posterior rays, by thin webs of bone in which
th e re may be additional smaller rays. The dorsal ray is a thick s tout process, which is concave on
its dorsal edge and there articulates with the large articular surface on the outer end of the horizontal
arm of the ectethmoid. The anterior ray is a pointed process, and rests upon and is strongly bound
b y ligamentous tissue to the lateral (distal) portion of the dorsal surface of the ligamentary process
o f the maxillary. The posterior ray is a sharp or rounded process which fits against, and is rigidly
bound to, the outer surface of the anterior end of the second bone of the series. Two of the remaining
rays form two of the sharp spines characteristic of th e fish, the one directed ventrally and the other
antero-ventrally, from the ventral edge of the bone. The sixth ray, when present, lies in the web