Thé SUPRAPREOPERCULAR is in contact, by its ventral edge, with th e dorsal end of
th e preopercular, and is pa rtly traversed by, and in p a rt forms a bounding wall of th e dorsal end
of the.preopercular latero-sensory canal; b u t it lodges no organ of th a t canal. Its dorsal end lies
immediately behind th e posterior articular head of th e hyomandibular, and this end of the supra-
preopercular is firmly attached to a flange of bone th a t fills the obtuse angle between th e posterior
articular head of the hyomandibular and its opercular articular head, a circular passage being left
between th e two bones to transmit the dorsal end of th e preopercular canal. The coinciding dorsal edges
of the suprapreopercular, and the flange of th e hyomandibular to which it is attached, form a broad
surface which is slightly concave, is marked with transverse striae, and articulates with th e lateral
edge of th e pterotic. The articulation is, accordingly, in p a rt with a dermal bone, probably of latero-
sensory origin, and in p a rt with a portion of th e hyomandibular th a t is apparently of membrane
origin. This la tte r articulation, with a portion of th e hyomandibular th a t is apparently of membrane
origin, is found alone, b u t much more developed, in Dactylopterus. The intimate attachment of
th e suprapreopercular to th e hyomandibular has n o t only completely blocked th e passage for the
dilatator operculi muscle, b u t has cu t th a t muscle into anterior and posterior portions, as already
described.
The anterior and posterior articular heads of the hyomandibular lie close together, on the
dorsal end of the bone, separated by a narrow roughened surface th a t has th e appearance of dermal
bone. The opercular articular head is long and slender, and is connected, b y a wide web of bone,
with th e ventral portion of th e shank. The bone is traversed by th e canal for th e hyoideo:mandibularis
facialis, a single small branch canal transmitting a nerve destined to innervate, as in the other fishes
described, certain organs in th e preopercular.
The SYMPLECTIC is a slender bone, with a flattened distal end which lies in th e symplectic
groove on th e inner surface pf the quadrate. Between this flattened distal portion and th e proximal
end of th e bone, th e symplectic arches slightly, leaving a long b u t narrow space between itself and
th e preopercular, this space transmitting th e ramus mandibularis externus facialis and th e arteria
hyoidea. The mandibularis intemus facialis passes anterior to th e symplectic, between th a t bone
and th e hind edge of th e quadrate, as in th e other fishes of th e group.
The hyomandibulo-symplectic interspace of cartilage lies in th e little concave surface ip the
angle between th e dorsal and ventral limbs of th e flange on th e inner surface of th e preopercular,
as already stated, b u t it occupies only th e dorsal portion of th e concavity. Ventral to it, the
remainder of th e concavity lodges th e small interhyal, th a t element articulating with th e cartilage
in a little facet on its ventro-posterior surface. In th e comer between th e cartilage, th e inner surface
of th e preopercular, and th e ventro-posterior comer of th e hyomandibular, there is a small opening
which transmits th e ramus hyoideus facialis.
The QUADRATE has a well developed posterior process, and on th e lateral surface of the
postero-ventral edge of this process there is a wide, fla t flange. This flange projects dorso-laterally
a t an acute angle to th e flat, plate-like body of th e bone, and its anterior end is prolonged forward
beyond th e anterior edge of th e body of th e bone as a strong anterior process. The ventro-posterior
surface of th e body of the flange fits, in larger part, against the internal surface of th e ventro-anterior
end of th e preopercular, in th e angular groove between th e body of th e bone and th e ventral limb
of th e flange on its internal surface; b u t a small anterior portion of this surface fits against th e internal
surface of th e th ird bone of the infraorbital series. The anterior prolongation of the flange rests
upon and is firmly bound to the internal surface of the ventral limb of the second infraorbital bone.
The posterior process of th e quadrate occupies the anterior half only of the ventral limb of th e angular
groove on the preopercular, and-the articular head of the bone projects beyond th e anterior end of
th e preopercular and is there exposed on the external surface of th e apparatus in an angular notch
in th e ventro-anterior corner of th e preopercular. On th e internal surface of the quadrate, there is
a shallow symplectic groove.
The METAPTERYGOID has a long and slender dorso-posterior process, the dorsal end of
which closely approaches and is bound by tissue to a th in web of bone on the anterior edge of th e hyo-
mandibular; this process thus being the internal flange on th e hind edge of the bone. At the
base of th e process there is a slightly developed external flange, the hind edges of both flanges being
widely separated from th e anterior edge of the hyomandibular. In the V-shaped space between
the two flanges a portion of th e levator arcus palatini has its insertion. The ventro-anterior edge
of the bone is everywhere separated from the quadrate by a narrow line of cartilage, the posterior
corner of this edge of the bone being in contact with the symplectic.
The ENTOPTERYGOID is a small, th in plate of bone which lies in the membrane th a t covers
the ventral surface of th e adductor arcus palatini muscle. Its ventral edge rests against the inner
surface of the narrow band of cartilage th a t lies .between th e quadrate and metapterygoid, usually
extending forward slightly beyond th a t cartilage onto the inner surface of the ectopterygoid. Its
hind edge overlaps slightly th e inner surface of the metapterygoid.
The ECTOPTERYGOID is a stout bone, with the usual dorsal and ventral limbs lying a t an
angle to each other. The two limbs of th e bone form a th in plate, which is completely ankylosed,
a t th e angle between th e two limbs, with a plate of bone which is certainly of separate origin, and
which has been already referred to as th e dermo-ectopterygoid. The ventral limb of the bone has
the usual position along the internal surface of th e anterior edge of the quadrate, the dorsal limb
lying along th e v entral and outer surfaces of th e hind end of th e palatine, and also along the same
surfaces of the palatine cartilage.
The DERMO-ECTOPTERYGOID lies on th e external surface of the th in plate formed by
the two limbs of th e membrane-ectopterygoid, and extends from th e angle between th e two limbs
of th a t bone forward along the dorsal limb. I t projects dorsally beyond th e membrane-ectopterygoid,
along th e lateral surface of th e enlarged posterior portion of th e palatine cartilage, and then beyond
th a t cartilage, there forming an important angle in the apparatus. The ectal surface of th e bone
is presented dorso-laterally, and th e posterior half of this surface lies against and is firmly bound
to th e inner surface of the antero-dorsal corner of the third infraorbital bone. A small anterior portion
of the plate lies against b u t is much less firmly bound to th e inner surface of th e hind end of the
dorsal limb of the second infraorbital bone. Between these two surfaces of contact with th e infraorbital
bones, the outer surface of th e plate is granulated and comes to th e level of and forms p a rt of the
outer surface of the bony cuirass of th e cheek. The dorsal edge of the p late is presented dorso-mesially,
and its thick posterior portion is grooved, the groove articulating with th e articular ridge near the
hind end of the lateral edge of th e ectethmoid. Anterior to this groove the dorsal edge of the plate
is thin, and lies against the lateral surface of the rod of palatine cartilage, the la tte r cartilage not
coming into articular relations with the ectethmoid. On this thin portion of th e dorsal edge of the
Zoologies. H efc 57. 2 0