lateral edge of th e parieto-extrascapular, th a t bone n o t overlapping th e suprascapular a t all. The
remainder of th e anterior edge of the bone suturates with th e lateral extrascapular and pterotic.
The bone is traversed by th e main infraorbital latero-sensory canal and lodges one organ of th a t
canal. The canal leaves th e bone b y a large opening on its lateral edge, near its hind end, and immediately
anterior to this opening, on the ventral surface of th e bone, th e wide s tout opisthotic process
arises. Immediately postero-mesial and also immediately postero-lateral, to th e hind edge of the
base of th e opisthotic process, there are small articular facets. These two facets give articulation to
two articular eminences on the dorsal edge of th e supraclavicular, these eminences embracing the
hind edge of th e opisthotic process of the suprascapular. From the deep layers of th e hind edge of
th e epiotic region of th e bone there projects postero-mesially a thick p late of bone w hich gives support,
on its dorsal surface, to the first one of th e series of dorsal plates on the body of th e fish.
The SUPRACLAVICULAR is a somewhat triangular bone, the external surface of which is
slightly concave and pa rtly covered with small granulations. On its short dorsal edge, which represents
th e base of th e triangle, are the two little eminences, above referred to, which articulate with
the suprascapular. Posterior to these eminences, th e dorso-posterior corner of th e bone is traversed
by th e main latero-sensory canal, and lodges one organ of th a t canal. The ventral end of th e bone is
pointed, instead of being expanded as in Trigla, b ut, as in th a t fish, it overlaps externally and is
bound to th e dorsal end of th e clavicle; and, excepting th a t the bone is relatively smaller th a n in
Trigla, there is nothing abnormal in its position or relations to the other bones.
The PARASPHENOID has th e shape shown in th e figures. The ascending process of either
side rises a t about the posterior q u a rte r of th e length of th e bone, and is a th in triangular plate th a t
lies transversely to the axis of th e bone instead of parallel to th a t axis. The point of the triangle is
directed upward and the base downward, and from this base of th e triangle a th in flange of bone
extends forward along th e lateral surface of th e bone. The mesial edge of th e triangle is thickened
somewhat, is directed dorso-latero-posteriorly and terminates in a sharp point; and this thickened
p a rt alone of the triangle would seem to be th e homologue of th e entire ascending process of th e bone
in the other fishes so far described, for it alone lies between the anterior edge of th e posterior
portion of th e body of the bone and the hind end of its thickened interorbital portion. The triangular
plate can accordingly be considered as a th in flange of bone th a t arises from th e lateral surface of the
ascending process proper; this flange projecting laterally and slightly posteriorly, and, a t the ventral
end of th e process, being b en t forward, in a rounded angle, and then continued forward as a flange
th a t projects laterally and slightly ventrally from the ventral edge of the lateral surface of th e interorbital
portion of the bone.
On th e dorsal surface of the interorbital portion of th e parasphenoid, two th in laminae of bone
arise, and converging posteriorly, unite, slightly anterior to th e ascending processes of the bone, to
form a median tooth-like process. The triangular space between th e two laminae lodges, as in Trigla,
the ventral end of th e cartilage of th e interorbital septum, the hind end of the process giving a tta ch ment
to membrane th a t represents th e leg of th e basisphenoid; th a t bone being w anting in Peristedion.
On the dorsal surface of th e posterior portion of th e parasphenoid there is a median longitudinal
raised portion which is deeply grooved on its dorsal surface. This raised portion fills th e hypophysial
fenestra, th e groove on its dorsal surface forming p a rt of th e floor of the myodome. The hypophysial
fenestra extends backward slightly beyond the anterior edge of th e basioccipital.
There is no BASISPHENOID bone, as ju s t above stated, nor is there an ORBITOSPHENOID.
The ALISPHENOID is bounded by the prootic ventrally, the frontal dorsally and the sphenotic
postero-laterally. Its anterior edge forms th e dorsal half of the large orbital opening of th e brain
case, this edge of th e bone being, because of th e flattening of th e hind wall of the orbit, presented
almost directly mesially. ■ There is no indication of a parasphenoid leg to the bone. On th e dorsal
half of th e inner surface of th e bone there are two brace-like thickenings, the larger one of which
underlies the antero-lateral corner of th e postepiphysial interspace of cartilage, while the other forma
the dorsal end of the anterior wall of the labyrinth recess. The mid-brain recess lies between the two
braces. The anterior edge of th e bone is either notched, or perforated by a small foramen which
must transmit th e anterior cerebral vein, though this vein was not traced in the dissections. Not
far from th e ventral edge of th e bone a small opening leads into a canal which traverses the bone and
transmits th a t branch of the ophthalmicus lateralis th a t innervates the terminal organ of the supraorbital
canal.
The SPHENOTIC is bounded by th e alisphenoid, prootic and pterotic, and gives support,
on its dorsal surface, to th e frontal and postfrontal bones. Its dorso-lateral corner comes to the level
of the dorsal surface of th e secondary skull, and has surface markings similar to those on th e adjacent
dermal bones. Between it and th e prootic there is a deep facet for the anterior articular head of the
hyomandibular, while, posteriorly, between the sphenotic and the pterotic, there is a small dilatator
fossa. The bone is traversed by a canal for the ramus oticus facialis, as in Scorpaena.
The DILATATOR OPERCULI,;,it may here be stated , is found in anterior and posterior
portions which are separated from each other b y the complete fusion of a suprapreopercular bone with
the hyomandibular. The anterior portion arises in the dilatator fossa, is fibrous, with b u t few muscle
fibers, and is inserted on the suprapreopercular and th e adjoining portions of the hyomandibular.
The posterior portion is muscular, arises from the posterior surface of the suprapreopercular and the
adjoining portions of the hyomandibular, ventral to the opercular process of th a t bone, and has its
insertion on the opercular. The fusion of the suprapreopercular with th e hyomandibular thus cuts
the originally continuous muscle into two portions.
The PROOTIC is bounded by the alisphenoid, sphenotic, pterotic, exo.ccipital and basioccipital
bones, its ventral edge being overlapped externally b y the parasphenoid. The opisthotic does not come
into bounding relations w ith it. The mesial process of the bone inclines strongly upward and corresponds
to the postpituitary portion, only, of the processes of Trigla and Scorpaena. The lateral corner of
th e anterior edge of the process is perforated by the foramen for the nervus abducens. The anterior
edge of the body of the bone is perforated, as in Trigla, by a large opening which is the facialis
opening of the imperfectly enclosed trigemino-facialis chamber. -This chamber forms a deep recess
on the orbital surface of the prootic, and from i t four foramina usually lead into the cranial cavity.
Two of these foramina are large, one of them lying directly dorsal to the other and being separated
from it by a delicate bar of bone. The other two foramina are small, one of them lying immediately
dorsal to the dorsal one of the two large foramina, and the other one anterior to the line of separation
between the two la tte r foramina. The dorsal one of the two large foramina transmits the nervus
trigeminus and ramus buccalis lateralis, the ventral one transmitting the nervus facialis. The small
foramen dorsal to the trigeminus foramen transmits the ramus ophthalmicus lateralis, this foramen
being sometimes fused with the trigeminus foramen. The other small foramen transmits th e ciliaris
Zoologica. Heft 57. 19