depression which gives articulation to the dorsal end of a long, slender, gutter-shaped and tapering
bone, which is applied to the antero-lateral surface of the dorsal end of th e clavicle and is certainly
the SUPRACLAVICULAR. This bone is not traversed by th e main infraorbital canal, and its
latero-sensory component must be represented either in a p a rt of the unusually large suprascapular
or in a small bone th a t lies along the postero-lateral edge of the suprascapular and is traversed by
the main infraorbital canal after it leaves th a t bone.
On either side of the hind end of the skull there is a large and deep fossa, already several
times referred to. This fossa occupies th e entire posterior surface of either side of th e skull, and has
deep dorso-mesial and dorso-lateral corners, or recesses, and a shallow ventral one. I t is bounded
by the mesial extrascapular, suprascapular, supraoccipital, epiotic and exoccipital, and there is nothing
comparable to it in any of th e other fishes of the group. Want of material prevented a proper
investigation of it, b u t it is largely, if n o t entirely filled by an anterior prolongation of th e swiin-
bladder; the dorsal wall of this portion of th e bladder lying close against the ventral surface of the
dermal bones th a t form the roof of th e fossa, and th e lateral surface of the bladder having closely
applied to it a band-like anterior prolongation of the tru n k muscles.
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 chain consists of four bones, all of which are traversed b y th e main infraorbital
canal. In addition to these four bones, there is a small bone, the pontinal of Gill, which extends
from the hind edge of the second bone of the series into a reentrant angle on th e anterior edge of the
preopercular.
The first infraorbital bone, or lachrymal, has a thickened anterior end which curves mesially,
and almost meets, in the middle line, its fellow of th e opposite side. The dorsal edge of this p a rt of
the bone is slightly grooved and articulates moveably with the antero-ventral edge of the nasal, the
dorsal edge of th e lachrymal lying upon and being strongly b u t somewhat loosely bound to the outer
surface of th e lachrymo-palatine process of th e nasal. In te rn a l to the hind end of this grooved
portion of th e lachrymal, there is, on th e internal surface of the bone, a short transverse ridge with
a convex outer edge, and slightly posterior to this ridge there is a second b u t shorter ridge; these
two ridges and th e groove between them having a sliding articulation with th e palatine on th e dorsolateral
surface of its maxillary process, as will be later explained. Slightly ventro-posterior to these
two articular ridges, a strong brace-like process arises from th e internal surface of th e lachrymal,
projecting dorso-postero-mesially. The dorsal end of this process is large, lies in the level of the
dorsal edge of th e bone, and has on its dorsal surface a large oval facet which articulates with the
lachrymal articular eminence of the ectethmoid. The hind edge of the articular facet suturates with
th e anterior edge of th e orbital shelf of th e second infraorbital bone, th e hind edge of the lachrymal
itself suturating with th e second and third infraorbital bones; th e second infraorbital lying ventral
to th e th ird one and having no bounding relations to th e orbit. The bone is traversed by the main
infraorbital latero-sensory canal and lodges three sense organs of th a t line.
The second infraorbital bone is an elongated one, bounded anteriorly by th e first and dorsally
by th e third bone of th e series. The main infraorbital canal enters it a t its anterior edge, runs horizontally
backward in it and then tu rn s upward and forward a t an acute angle, to leave the bone on
its dorsal margin and enter the th ird bone of the series; this section of canal lodging two sense
organs. The ventro-posterior comer of the hone is prolonged into a short process which has articular
surfaces for articulation with the pontinal.
The pontinal is a small and somewhat elongated bone, which extends from the second infraorbital
into a reentrant angle on the anterior edge of the preopercular, articulating with and being
firmly bound to each of these two bones. I t does not lodge any p a rt of' the latero-sensory canal,
and is accordingly either an independent dermal ossicle or a detached portion of the second infra-
orbital bone.
The third infraorbital bone bears, along the internal surface of its orbital margin, a large thin
projecting plate of bone which forms about one half of the floor and a corresponding p a rt of the posterior
wall of the orbit. The central portion of this orbital shelf is supported by a bracing web of bone
which arises from the internal surface of this bone and is continued beyond it onto the internal surface
o f the second infraorbital bone, near its hind edge. From th e internal surfaces of the adjoining edges
of these two infraorbital bones, immediately anterior to the bracing web, a strong ligament arises,
and running forward has its insertion on th e ventral surface of the dorsal limb of the dentary. The
anterior end of the orbital shelf projects forward beyond th e anterior edge of th e body of the bone,
along th e inner surface of the first infraorbital, and comes into sutural contact with, and is firmly
bound to, the hind edge of the dorsal end of the brace-like articular process of the la tte r bone. The
bone is traversed by the main infraorbital latero-sensory canal and lodges three organs of the.line.
The fourth infraorbital is a small bone, postorbital in position, th a t is in contact ventrally
with th e third infraorbital and dorsally with the postfrontal. I t transmits the latero-sensory canal
from the former to the la tte r bone, lodging one organ of the line.
The first and .third,infraorbital.bones are the preorbital and fourth suborbital, respectively,
of Gill s descriptions; and these two bones and the second infraorbital, together, form the first sub-
orbital of Cuvier and Valenciennes’ descriptions. The second suborbital of Cuvier and Valenciennes
is the third suborbital, or pontinal of Gill’s descriptions, b u t this bone, not being traversed by the
infraorbital canal, would seem n o t to properly be an independent element of the infraorbital series.
3. S U S P E N S O R I A L A P P A R A T U S A N D M A N D I B L E .
The bones th a t form the hyomandibulo-palato-quadrate apparatus are firmly united to form
two pieces with a flexible joint between them. The posterior and much larger piec<?is formed by
th e preopercular, hyomandibular, symplectic, quadrate and metapterygoid; and the anterior piece
by the palatine, the ectopterygoid and the entopterygoid. The flexible joint between the two pieces
is nearly transverse to the axis of th e body of the fish, and permits th a t extensive lateral motion
of the hind end of the apparatus th a t easily places the large preopercular spine a t an angle of more
th a n 45° to the axis of the body.
The PREOPERCULAR has a horizontal limb, which terminates in the long and well known
spine, and a vertical limb which extends antero-dorsally a t an angle of about 75° to the horizontal
limb. In th e angle between the two limbs there is an articular facet, and immediately dorsal to this
facet an articular eminence, both of which give articulation to corresponding surfaces on the hind
end of th e pontinal. The angle between the two limbs is spanned by a large web of bone which
arises from the deeper layers of the preopercular; and, external to this web, on either limb of the.
bone, between the web and the outer surface of th e thick, related limb, there is a large V-shaped