of bone th a t unites the dorsal and anterior rays, and th e anterior pore of th e main infraorbital canal
lies a t th e outer end of this ray, there opening on th e external surface of th e web of bone, close to its
dorso-anterior edge. On th e internal surface of th e bone, opposite or slightly anterior to this latero-
sensory opening, a stout ligament has its origin, and, running ventro-mesially, is inserted on th e
lateral surface of the dorsal edge of the maxillary process of th e palatine, opposite and immediately
anterior to th e surface of insertion of the rostro-palatine ligament. On the ventral edge of th e anterior
ray of the bone, usually close to its base, and hence between i t and th e anterior one of the two ventral
spines of the bone, is th e opening of th e second primary tube of th e infraorbital canal; and on the
ventro-posterior edge of th e anterior ventral spine, is th e opening of the third primary tube of the
same canal. On the posterior edge of th e posterior ventral spine, or on th e ventral edge of th e posterior
ray of the bone, th e position varying slightly, is th e opening of the fourth tube; this tube
lying between th e lachrymal and th e next posterior bone of th e series. Along th e internal surface
of th e posterior ray, th e main infraorbital canal passes from th e lachrymal into th e second bone of
the chain. The rays of th e lachrymal bone thus, all b u t one, have relations to the primary tubes
of th e latero-sensory system. The bone lodges three sense organs of th e infraorbital line.
The second infraorbital bone, is, in position, a first suborbital bone. I t is an elongated bone,
traversed by th e main infraorbital canal, and has primary tubes of th e line a t either end. I t lodges
a single infraorbital sense organ and hence is a single latero-sensory skeletal unit. A short spine
arises near the hind edge of th e bone, and projects backward above th e fifth infraorbital pore. This
spine is hardly noticeable in-young specimens of Scorpaena scrofa, or in either young or ad u lt
specimens of Scorpaena porcus.
The th ird infraorbital, or second suborbital, is, as Gill (’88) says, „hypertrophied and developed
as a s tay impinging on th e anterior wall of th e preopercular“. I t abuts against, and is firmly
bound by tissue to, a depressed line on th e anterior surface of th e outer edge of a strongly developed
ridge on the outer surface of the preopercular, opposite th e base of th e largest and most dorsal preopercular
spine. The bone is convex externally and concave internally, and in th e middle line of
its external surface there is a longitudinal ridge which marks th e position of the enclosed latero-
sensory canal. Near th e posterior end of this ridge, two primary tubes lead from th e canal to th e
outer surface of th e bone, one on th e ventral surface of th e ridge, and th e other, slightly posterior
to it, on th e dorsal surface of th e ridge; these tubes being, respectively, th e 6 th. and 7 th . primary
tubes of th e line. The bone lodges two infraorbital sense organs. A short spine projects backward
above the seventh infraorbital pore, th is spine, like the one on th e first suborbital, being unimportant
in young specimens and in Scorpaena porcus.
The postorbital bone is a small semi-cylindrical piece of bone th a t lies in th e dermis th a t
forms th e hind margin of the orbit, about midway between th e dorsal edge of th e third infraorbital
bone and th e postorbital comer of the skull. I t lodges a single latero-sensory organ, and is developed
in relation to th a t organ.
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 hyomandibular, symplectic, preopercular and palato-quadrate are all united or firmly
bound together, and form a single piece which articulates with the skull a t its anterior and posterior
ends and bears th e mandible.
Q U A D R A T E .
The quadrate is a quadrant-shaped bone with its ventral corner thickened to form an articular
surface for the mandible. The dorsal edge of the bone is wavy, and is bounded by cartilage
which separates it from the ventral edge of the metapterygoid. Its anterior edge is nearly straight,
is bevelled on its internal surface, and overlaps and fits against th e external surface of th e ventral
limb of th e ectopterygoid. Its posterior edge is slightly convex, is thickened and grooved, and fits
against th e anterior edge of th e ventral portion of the preopercular. This thick posterior edge of the
bone terminates dorsally in a short point, usually longer and sharper th an in the specimen used for
th e figures. This point fits against the inner surface of a th in flange on the anterior edge of the
preopercular, and between it and th e dorsal edge of the body of th e quadrate there is a curved notch.
This notch forms th e relatively wide dorsal end of a shallow and tapering groove on th e inner surface
of the bone, th e groove running downward and forward to th e thickened articular head of the
bone, where it ends in a slight recess. The groove lodges the ventral three-fifths of th e symplectic
and may be said to separate th e quadrate into two parts, a body and a posterior process. The groove
is everywhere wider th an th a t p a rt of the symplectic th a t lies in it, a channel thus being left on either
side of the la tte r element. A t the upper end of th e channel th a t lies anterior to th e symplectic, there
is a perforation of the apparatus, through which the mandibularis intemus facialis passes from the
outer to the inner surface of th e palato-quadrate, and then runs downward in th e channel along the
inner surface of the apparatus. At th e upper end of the channel th a t lies posterior to th e symplectic,
th e mandibularis externus facialis passes, in a similar manner, from th e outer to the inner surface
o f th e apparatus, the arteria hyoidea traversing the same opening.
The posterior process of the quadrate of fishes-is a feature of some morphological importance.
I t is n o t found, as a p a rt of the quadrate, in the bony ganoids, b u t is found in most, if not all teleosts.
I t probably is present in all th e Acanthopterygii and Anacanthini, for it is shown in all th e figures
th a t I can find of the quadrate of those fishes. In Siphonostoma, of th e Lophobranchii, it would
seem to be certainly present, though Supino’s figure (’06) is not very definite in this particular. In
Balistes, of th e Plectognathi, I find it in normal position, and it is shown by Bruhl (’56) both in this
fish and in Diodon. Among the Physostomi, of Gunther’s classification, it is shown in Belone
(Swinnerton, ’02), Esox (Swinnerton, ’02), Galaxias (Swinnerton, ’03), Salmo (Parker, ’73), Hyodon
(Ridewood, ’04 b), Osteoglossum (Ridewood, ’05 a), Megalops (Ridewood, ’04 a), Alepocephalus
(Gegenbaur, ’78) and Notopterus (Ridewood, ’04 b). In Ameiurus (Me Murrich, ’84), Silurus (Jaquet,
98) and Erythrinus (Sagemehl, ’84 b) it seems to be present, in a modified form, as a short process
th a t gives support to the lower end of the preopercular. In Carassius auratus, I find it as a short
b u t normal process, a short groove here lodging a short terminal portion of th e symplectic. In
Ridewood’s figures of the Mormyridae (’04 b) it seems to be wholly absent, as it does also in most
•of th a t author’s figures of the Clupeoid fishes (’04 c); b u t Erdl (’47) apparently shows it in Gym-
narchus, and I find it perfectly normal, though small, in Clupea harengus. In the Muraenidae, which
I am investigating, I am of the opinion th a t both this process and th e symplectic are indistinguishably
fused with th e quadrate, and it may be th a t this same fusion has taken place in other fishes where
these two structures seem to be wanting. In Erythrinus Sagemehl says (’84 b, p. 92) th a t the symplectic
and quadrate are so closely united th a t even the lines separating th e bones are nearly lost,
th is evidently representing a stage in th e complete fusion of these bones.