The membrane in which they develop is, in my 45 mm specimens, a thick layer of coarse fibrous
tissue which extends from the opticus to th e abducens foramina, passing on either side of th e p ituitary
fossa. This membrane is continuous, on either side, with th e side wall of the skull, the ventral and
larger portion of th a t wall here being also of membrane. This la tte r membrane is attached dorsally
to the ventral edge of a cartilaginous process of the auditory capsule which forms th e dorso-lateral
corner and th e dorsal portion of th e side wall of this p a rt of th e skull. This process is called by
Swinnerton (’02), in his descriptions of Gasterosteus, th e postorbital process of the auditory capsule;
but, as already stated, supraorbital process would seem a b e tte r term, for th e process extends antero-
mesially from th e postorbital process of the skull along the dorsal edge of th e posterior portion of
the orbit. The membranous side wall of the skull ventral to this process is, in my 45 mm specimens,
undergoing ossification to form parts of th e prootic and alisphenoid bones, and th e former bone,
or th a t p a rt of the membrane th a t will ossify as p a rt of it, is perforated, immediately ventral to the
ventral edge of the cartilage, by two foramina. One of these foramina is a large opening which transmits
th e united trigeminus and lateralis trigemini nerves and also th e encephalic branch of the jugular
vein, the other transmitting th e facialis and lateralis facialis nerves. Ventro-anterior to these two
foramina, b u t still posterior to the slightly developed basisphenoid bone, th e membrane is pierced
by both th e oculomotorius and truncus ciliaris profundi; these two perforations lying relatively
close together, th e one for the ciliaris profundi slightly dorso-posterior to th e one for the
oculomotorius.
In the region ventral to th e profundus foramen th e membranous cranial wall is connected
by a bridge of dense, coarse, fibrous tissue, with the dorsal end of th e ascending process of th e para-
sphenoid, th a t p a rt of th e la tte r process th a t is cut in sections passing through this region, forming
the lateral wall of the orbital opening of the myodome and lying anterior to th e cartilage th a t represents
the ventral portion of the prootic. The dorsal end of th e process of the parasphenoid here lies
a t a relatively considerable distance from th e membranous side wall of the cranial cavity, and from
its anterior edge, and continuous with th e bridge of fibrous tissue th a t spans the space between it
and th e membranous cranial wall, a strong line of tissue runs dorsally, and, separating into two parts,
has its attachment to th e cranial wall, one p a rt dorsal and the other ventral to the ophthalmic nerves.
This line of tissue lies wholly anterior to the truncus maxillo-mandibularis trigemini, and represents,
in part, the two little process-like ridges on th e external surface of the alisphenoid of th e adult, and,
in part, the fibrous or connective tissues th a t extend from those little processes to the dorsal end of
th e ascending process of th e parasphenoid. The line of tissue th a t has its insertion dorsal, and hence
morphologically postero-lateral, to th e ophthalmic nerves, represents the postero-lateral one of the
two processes of the adult, th e line th a t has its insertion ventral, and hence morphologically antero-
mesial to th e nerves, representing th e antero-mesial process: th e two bands of tissue together representing
th e parasphenoid leg of the alisphenoid, here pierced by th e ophthalmic nerves, as the pedicle
of th e alisphenoid is in Amia. The basisphenoid leg of th e alisphenoid is represented in an undefined
portion of this p a rt of th e cranial wall, th a t wall being of membrane in its v entral portion, b u t already
ossified in its dorsal portion. The bridge of fibrous tissue th a t spans the space between these two
legs of th e alisphenoid, represents th a t p a rt of the orbital surface of the prootic of th e ad u lt th a t is
occupied b y the internal jugular groove.
Slightly posterior to the oculomotorius and profundus foramina th e lateral edge of the bridge
of fibrous tissue above referred to sends a line of tissue downward internal to, and parallel to the
bony ascending process of th e parasphenoid, this line of tissue edging the anterior edge of the plate
of cartilage th a t represents th e ventral portion of the prootic and then passing downward along the
external surface of th a t cartilage. From th e mesial edge of the bridge of tissue, and from the membranous
cranial wall posterior to it, another line of tissue descends, passing along th e internal surface
of the prootic cartilage. Between the two descending lines of tissue, anteriorly, and between the
prootic cartilage and the internal line of tissue posteriorly, a space is left, which, in the 45 mm specimens,
is filled with fa t globules and loose connective tissue. This space lies immediately beneath
the trigemino-facialis chamber, and its dorsal wall ossifies to form the thin bony floor of th a t chamber.
In its anterior portion th e space is tall, extending from th e floor of the trigemino-facialis chamber
downward beyond th e line of origin of the mesial process of the prootic; th a t process here being
wholly of membrane, and rising perpendicularly from the membranous mesial wall of the space.
Slightly posterior to this, in those sections th a t cut through the trigeminus foramen, the fa t space
separates into dorsal and ventral limbs. The dorsal limb continues backward immediately beneath
th e floor of the trigemino-facialis chamber and extends to the hind end of th a t chamber. The ventral
limb extends backward to th e h ind end of the prootic cartilage, lying always opposite the line of origin
of th e m embranous portion of the mesial process of the prootic, b u t passing v entral to the cartilaginous
portion of th a t process and there occupying th e dorso-lateral corner of the myodome. The lateral
wall of the dorsal limb of the space is always formed of membrane or of membrane bone. The lateral
wall of the v entral limb is always of cartilage, this limb of th e space lying in a wide and shallow groove
on th e inner surface of the prootic cartilage, the dorsal edge of the groove being marked by a sharp
edge or ridge.
This space in th e prootic evidently has some special morphological significance, for, although
not evident in the ad u lt Scorpaena, it quite certainly has its homologue in an important vacuity found
in the prootic of the adults of certain other teleosts, as will later be shown when describing the myodome
in Gadus. I t may be referred to as the prootic vacuity. The mesial wall of the anterior p a rt of the
vacuity is, in the 45 mm Scorpaena, a direct v entral continuation of the mesial wall of the trigemino-
facialis chamber, the lateral wall of this anterior p a rt of the vacuity being similarly related to the
lateral wall of th a t chamber.
Close to the anterior end of the prootic vacuity, in the 45 mm Scorpaena, the ramus palatinus
facialis pierces the membrane th a t later ossifies as the mesial process of the prootic, near the base
of th a t process, and passing internal to the anterior edge of the prootic cartilage enters the myodome.
The nerve arises from the intracranial communis ganglion, and does not in any p a rt of its course enter
the trigemino-facialis chamber. In the intracranial p a rt of its course, it lies along the cerebral surface
of a membranous portion of th e cranial wall, imbedded in loose connective tissues, these same tissues
also enclosing, mesially, the intracranial portion of the trigemino-facialis ganglion, and being prolonged
dorsally as p a rt of the cerebral wall of the labyrinth recess. This tissue may therefore represent the
tough glistening membrane th a t, in Amia, forms the lateral bounding wall of the cranial cavity in
the pituitary region, though it seems more probable th a t th a t membrane is represented, in Scorpaena,
in the membrane th a t forms the mesial wall of the trigemino-facialis chamber. Following Sagemehl,
I (’97) formerly considered th e tough glistening membrane of Amia as a specially developed portion
of the dura mater. My present work leads me to accept this conclusion only with the proviso th a t the
dura mater is itself a differentiated portion of the membranous tissue th a t primarily forms th e enclosing
capsule of the central nervous system.
Zoologica. Heft 67. <7