I n Hydrocyon also, both articulations are wanting, according to Sagemehl (’84 b, p. 95), and in th e
Cyprinidae, according to th e same author (’91, p. 582), the posterior articulation is replaced by an
articulation of th e entopterygoid with th e ectethmoid.
O P E R C U L A R BO N E S .
The opercular is so firmly bound by articular ligaments to the stout opercular articular head
of the hyomandibular th a t it is capable of but little movement. From its articular head a stout raised
portion runs posteriorly or postero-ventrally across the outer surface of the bone and terminates
in the stout opercular spine; the point of th a t spine extending slightly beyond the point of the large
preopercular spine and lying slightly dorsal to it.
The subopercular is an angular bone th a t embraces the ventral corner of the opercular. I t
bears a short, small spine at its ventral corner.
The interopercular is long and tapering. Its broad hind end is bound by tissue to the ventral
portion of the anterior edge of the subopercular, but it is separated from th a t edge by a considerable
interval, bridged by a connecting sheet of tissue. Its pointed anterior end is bound by ligament to
the lateral surface, of the hind end of the mandible.
m a n d i b l e :
The mandible is long and rather slender, and has angular, articular and dentary elements
th a t offer no special peculiarities. The dentary lodges three latero-sensory organs, and the articular
one organ. The summit of the coronoid process of the articular is separated by a considerable interval
from the hind end of the dorsal limb of the dentary, the intervening space being filled by a tough
pad of fibrous tissue. In the mandibular labial fold there is a gristly core, as in Scorpaena, but it is
smaller than in th a t fish.
4. M U S C L E S .
The adductor mandibulae of Cottus resembles closely th a t of Scorpaena. The superficial
division, Aj, of the muscle arises from the anterior portion of . the external surface of the
preopercular and runs almost directly forward, lying external to. the levator arcus palatini and to
the deeper division, A2A3, of the adductor. I t terminates anteriorly in a tendinous band which extends
the full length of its anterior edge and is inserted dorsally on the maxillary, while ventrally
it joins and becomes part of the tendon A2A3. The deeper division of the muscle, A2A3, is incompletely
separated into superficial and deeper portions, the superficial portion, A2, lying superficial
and ventral to the levator arcus palatini and the deeper portion lying internal to th a t muscle. The
two muscles have their origins, as in Scorpaena, from the anterior portion of the external surface
of the preopercular, ventral to the muscle Av and from the external surface of the palato-quadrate
apparatus. Running almost directly forward, certain fibers of the muscle pass directly into the
mandible and are continuous with the fibers of A0), others are inserted on the ventral end of the
tendinous band th a t edges the anterior end of the muscle Ax, while the larger portion have their
insertion on a tendinous structure th a t forms on i;he inner surface of the muscle and runs forward
and downward into the mandible. In the mandible this tendon separates into four portions, two
of which give origin to the fibers of Aw, the other two lying one external to the other and having
.their insertions on the internal surface of the articular near the hind end of Meckel’s cartilage. From
S i n m
this tendon, a, liganténtow'band runs backward and is inserted on the. internal surface
of the quadrate.
The levator arcus palatini runs downward internal to A1 and then internal to A2, lying always
external to A3 and also always external to the palato-quadrate. The course of the muscle is thus
in accord with the conclusion, already stated, th a t the dorsal portion of the hind edge of metapterygoid
of Cottus represents the inner one of the two flanges on the hind edge of the metaptérygoid of
Scorpaena, ■
. The dilatator operculi arises partly in the dilatator fossa, but mainly on the external surface
of the dorsal end of the hyomandibular and on adjacent portions of the preopercular, and is inserted
on the opercular as in Scorpaena.
The adductor hyomandibularis, and adductor and levator operculi are as in Scorpaena, but
the latter muscle is represented by several separate bundles of muscle fibers all of which extend from
the dorso-lateral edge of the skull to the dorsal edge of the opercular or subopercular; the posterior
bundles being delicate bands lying in the membrane th a t closes the dorsal end of the opercular
opening.
5. L A T E R O - S E N S O R Y C A N A L S .
The main infraorbital canal of Cottus traverses the four infraorbital bones without interruption,
and then enters and traverses the postfrontal, at the dorsal end of which it anastomoses
with thei penultimate tube of the supraorbital canal. I t then turns sharply backward and traverses
in succession the pterotic, lateral extrascapular, suprascapular and supraclavicular. The lachrymal
lodges two sense organs of the line; the first suborbital bone lodges two regular organs and, in the
one specimen examined, what was apparently a much smaller and additional organ between the
two regular organs; the second suborbital bone lodges two organs; and the postorbital bone one
organ: all of these organs being innervated by branches of the buccalis lateralis. The number of organs
in this part of the line, excepting the small and apparently supplemental organ in the first suborbital,
is thus exactly the same as in Scorpaena, but the third latero-sensory ossicle has, in Cottus, fused
with the fourth ossicle and so forms part of the first suborbital bone instead of fusing with the first
and second ossicles to form part of the lachrymal.
The postfrontal lodges one organ, innervated by a branch of the oticus lateralis; the pterotic
two organs, one innervated by the oticus lateralis and the other by a branch of the supratemporalis
lateralis vagi; the lateral extrascapular and suprascapular one organ each, innervated by branches
of the supratemporalis lateralis vagi; and the supraclavicular one organ, innervated bv the first
branch of the lateralis vagi. This part of the line thus differs from that in Scorpaena only in that
the pterotic lodges an organ innervated by the lateralis vagi; the dermal component of th a t bone
thus being formed by the fusion of two latero-sensory ossicles.
The supratemporal commissure lodges two sense organs on either side, one lying in the lateral
cxtrascapular and the other in the parieto-extrascapular, both innervated by branches of the supratemporalis
lateralis vagi.
The supraorbital canal traverses the nasal and frontal bones, and anastomoses by its penultimate
primary tube with th a t infraorbital tube that lies between the postfrontal and. pterotic bones.
The canal contains six sense organs, one lying in the nasal and five in the frontal, all innervated by
branches of the ophthalmicus lateralis. A primary tube leaves the canal between each two adjoining