dentary lodges four organs of the sensory line and th e articular, one. Primary tubes leave the canal
a t either end of th e angular, and four tubes leave it as it traverses th e dentary, one of these tubes
being th e anterior terminal tube of the line.
The dentary has the usual dorsal and ventral limbs, separated by a deep V-shaped reentrant
angle. The dorsal edge of the dorsal limb is lined its full length with villiform teeth. Immediately
ventral to this edge, on the outer surface of the bone, and a t about the middle of its length, there
is a large and deep depression which lodges and gives insertion to the base of a tapering gristly
structure which projects posteriorly and forms the core of the mandibular labial fold. This gristly,
semi-cartilaginous structure is attached, a t its hind end, by dermal tissues to the inner surface of
the hind end of the maxillary, and would seem to be the homologue of the labial cartilage of Swinner-
ton’s descriptions of Gasterosteus.
The angular is a small bone which forms the postero-ventral corner of the mandible. Its dorsal
end is united by synchondrosis with the articular, immediately ventral to the articular facet for
the quadrate, a small interspace of cartilage here being visible on the inner surface of the mandible.
The angular gives insertion to a short but strong ligament which has its insertion on the ventral end
of the interopercular, and also gives insertion to certain of the ligamentous articular tissues th a t bind
the mandible to the quadrate. There is, as in Scomber, no evident ligamentum mandibulo-hyoideum.
The articular has a s tout coronoid process, th e base of which forms th e anterior portion of
the articular facet for th e quadrate. The dorsal end of th e process lies slightly postero-ventral to the
hind end of the dorsal limb of th e dentary, and th e two bones are here connected by a pad-like struc tu
re of tough fibrous tissue which extends forward a short distance along the lateral and dorsal surfaces
of the hind end of th e dorsal limb of th e dentary. This pad forms, in the recent state, a
pronounced feature of the mandible, and the inner surface of th e maxillary slides against it as th e
mouth is opened and closed. The maxillo-mandibular ligament, as already described, runs across
th e external surface of this pad of tissue, with apparent interchange of fibers, and has its attachment
to the external surface of th e base of th e coronoid process and the adjoining portions of th e articular.
On the hind edge of th e articular a s tout curved process, projecting dorsally, forms the posterior
half of th e articular facet for th e quadrate. The dorsal end of this process gives insertion to a short
s tout ligament which extends anteriorly and has its origin on the adjacent lateral edge of th e articular
head of the quadrate. The mesial or postero-mesial surface of th e process is smooth and slightly
convex, is covered with a th in layer of fibrous or fibro-cartilaginous tissue, and, when th e mouth
is opened and shut, slides upon a p a rt of the hind edge of the quadrate immediately dorso-posterior
to the articular head of th a t bone; the outer, dorso-posterior end of th e process finally abutting
against a p a rt of th e quadrate, and so limiting th e opening movement of th e mandible. This sliding
articulation of this process of the articular is with the posterior process of the quadrate, and not
with th e body of th a t bone, and manifestly recalls the mandibulo-symplectic articulation of Amia,
to which reference was made when describing th e quadrate. In Scomber a similar sliding articulation
doubtless exists, b u t, when describing th a t fish (’03, p. 157) I did n o t recognize it, or its probable
homology.
On the internal surface of the articular, the hind end of Meckel’s cartilage is continued backward,
for a short distance, as a bony ridge which presents the appearance of a posterior and ossified
continuation of that cartilage. On the dorsal surface of this ridge, and partly immediately anterior
to it, the tendon of the deeper part of the adductor mandibulae has its insertion.
4. A D D U C T O R M A N D I B U L A E A N D L E V A T O R A R C U S P ALAT I N I
M U S C L E S .
The-adductor mandibulae is completely separated into dorsal an d mandibular portions. The
dorsal portion is a large muscle, almost completely separated into two divisions, a superficial and a
deeper one. The superficial division is apparently the homologue of the muscle A, of Vetter’s descriptions
of other teleosts, the deeper division representing the two muscles Aa and A3 of the same
descriptions. The mandibular portion of the muscle is the muscle A,, of Vetter’s nomenclature, and
lies wholly in th e mandible.1 The mandibular branch of the nervus trigeminus, in its course to enter
th e mandible, passes between the muscles A, and Aa As.
The muscle Aa arises from the outer edge of th e preopercular, there lying, in its dorsal portion,
directly external to th e levator arcus palatini, and in its Ventral portion directly external to a portion
o f ; Aa A3. The fibers of th e dorsal two-fifths, approximately, of th e muscle do not reach the preopercular,
being inserted on a broad th in tendinous band which crosses the outer surface of the
levator and has its insertion on the preopercular. The fibers of the muscle all run forward in a nearly
parallel Course, and are inserted on a tendinous band th a t extends the full length of th e anterior
edge of th e muscle. The dorsal end of this band becomes a short stout tendon which has its insertion
on the mesial surface of th e shank of the maxillary, the ventral end of the band joining the tendon
o f th e muscle Aa A3. The anterior edge of th e tendinous band gives,uttachment to the fibrous tissues
th a t line the lateral surface of th e mucous membrane th a t extends from the ventral edge of the palato-
q uad ra te to the internal surface of the maxillary, and it is in this fibrous tissue th a t the maxillomandibular
ligament, already described, has its course, lying close/along the anterior edge of the
muscle A,. This maxillo-mandibular ligameni|'4rust accordingly be acfed.omby the muscle Aa, and
hence serves in p a rt as its tendon of insertion; a contraction of the ventral fibers of Ar rotating the
maxillary. In Scomber th e tendon of A, is inserted on the internal surface of the lachrymal, the
maxillo-mandibular ligament in p a rt giving insertion, to th e deeper portion, A3, of the adductor
(Allis, ’03, p. 192).
The muscle AaA3 is much thicker and stouter th a n Aa, and has its origin on the external
surface of the body of th e metapterygoid, near its hind edge, and, ventral to the metapterygoid, on
th e anterior surface of the preopercular. The muscle is incompletely separated into dorso-intemal
an d ventro-external portions which may represent As and Aa respectively, the fibers of As all passing
internal to the external bundle of the levator arcus palatini, while the fibers pi Aa pass external
to or lie wholly ventral to th a t muscle. The fibers of both portiqns of th e muscle a t first converge
slightly forward, and then contract rapidly,- and are all, or nearly all inserted on a large tendon
which passes into the mandible. The few fibers th a t are sometimes not so inserted form a broad, thin
superficial sheet, the fibers of which separate from th e deeper fibers of the muscle and have their
insertion in a tendinous formation on the inner surface of the muscle Ar The large tendon Aa Aa
separates into three parts. The middle one of these three parts arises mainly in relation to the
fibers of As, the.other two arising mainly in relation to the fibers of Aa and Aa these two tendons
lying the one postero-ventral and the other antero-dorsal to the middle tendon. The middle tendon
Tuns downward and forward, and has. its insertion on the mesial surface of the articular immediately
dorsal, to the hind end of Meckel’s cartilage. The postero-ventral tendon runs forward and downward
across the lateral surface of the middle tendon, and then turns ra the r sharply downward, passes