1. The mesethmoid processes of fishes are processes of th e mesethmoid bone, or of the
ethmoid cartilage, th a t give origin to th e ethmo-maxillary ligament, and th a t support or give
attachment to the hind end of the nasal of either side. In the Loricati they are prominent processes
of the mesethmoid; in Trigla and Peristedion they are small processes of th e same bone, wholly
concealed beneath the nasals; while in Dactylopterus they are small processes of the ethmoid
cartilage.
2. The dilatator, temporal and supratemporal fossae of fishes are grooves on th e dorsal surface
of the primary cranium, more or less completely roofed b y dermal bones. Each of these grooves may
have an anterior extension th a t lies upon th e outer surface of the dermal bones of th e roof of the skull,
as in Scomber. In th e mail-cheeked fishes, these anterior extensions are not found, b u t the areas
occupied by them in Scomber are represented, on either side of th e dorsal surface of the skull of the
Loricati, by contiguous regions bounded by four more or less developed ridges th a t radiate approximately
from th e frontal spine. The ridge between th e anterior extensions of th e temporal and
supratemporal fossae is in a measure continuous with the epiotic ridge on th e posterior surface of
th e skull, and th e posterior semicircular canal lies internal to this la tte r ridge. The ridge between
th e anterior extensions of th e temporal and dilatator fossae is similarly continuous with th e ridge
th a t forms th e boundary between the posterior and lateral surfaces of the skull, and th e posterior
leg of the external semicircular canal lies internal to a portion of this ridge. The ridge forming
th e anterior boundary of the anterior extension of th e dilatator fossa is approximately continuous
with the ridge th a t separates the hind wall of th e orbit from the lateral surface of the brain case,
and the summit of the anterior semicircular canal lies in a measure internal to it. The position
of th e frontal spine, from which these several ridges radiate, corresponds somewhat to th a t of the
opening of the endolymphatic tube in selachians. The subtemporal fossa, on th e lateral surface
of the skull, lies between the external semicircular canal and th e utriculus.
The temporal fossa may have an epiotic diverticulum, and it may also have, as in Amia, an
anterior diverticulum. This la tte r diverticulum lies on the dorsal surface of the primary cranium,
beneath th e dermal bones of the roof of the skull, and in certain fishes (Elops, Albula) it becomes a
large and important portion of the fossa. B u t this anterior diverticulum of the fossa is n o t to be
confounded with the anterior extension ju s t above referred to, the former lying ventral and the la tte r
dorsal to th e dermal bones.
The anterior extensions of th e supratemporal grooves have coalesced in the Loricati to form
the subquadrangular groove on th e vertex.
3. The premaxillary of the mail-cheeked fishes has, on its anterior end, two processes, one of
which is th e ascending process properly so-called, and the other an articular process; b u t the two
processes together are usually referred to' as th e ascending process of the bone.
The articular process is probably the earlier acquisition of th e two, is apparently found in
all osseous fishes, and it, alone, is sometimes miscalled th e ascending process of the bone (Amia,
Salmo).
The ascending process is formed by the fusion with the premaxillary of a supraethmoid bone,
the la tte r bone being primarily developed in protective relation to a line of latero-sensory organs,
and being so found, not only in certain ganoids (Amia, Polypterus) b u t also in Elops and probably
in Belone, these two teleosts being the only ones in which it is known to occur. In Belone the bone
is indistinguishably fused with th e premaxillary, while in Elops it is found as an independent ossicK
4. The maxillary of th e mail-cheeked fishes has, on its anterior end, a process th a t may be called
its ascending process-. This process gives articulation to th e articular process of the premaxillary,
and itself articulates, by the intermediation of a pad of semi-cartilaginous tissue, with the dorsal
surface of th e ascending process of th e vomer. This process of th e maxillary is apparently found
in all the Acanthopterygii and Anacanthini of Gunther’s classification, b u t it is not evident in all
descriptions of the Physostomi. In those fishes in which it is found it varies greatly in its development,
and may even be found as two instead of as a single process.
5. The vomer of fishes is primarily a bone, doubtless paired, th a t is developed in relation
to tooth-bearing plates on th e dorsal surface of the mouth cavity; and it was primarily limited to
th e roof of th a t cavity. In certain teleosts, however, this tooth-bearing plate has acquired a dorsal
limb which may be said to consist of a head and two ascending processes, one on either side; and
these ascending processes are quite certainly formed by th e fusion, with th e tooth-bearing plate,
o f th e pre-ethmoid (septomaxillary, Amia) bone of either side. When th e pre-ethmoids are found
as independent ossifications the vomer is without ascending processes. The ascending process of
either side gives articulation to the ascending process of the corresponding maxillary.
6. The septomaxillary of the Amphibia and the higher vertebrates is probably represented
in fishes by the antorbital bone of Amia, th a t bone being developed in protective relation to the
infranasal portion of the latero-sensory canals. This antorbital, latero-sensory bone is found §p
Polypterus and Elops, as well as in Amia, and is possibly also found in certain of the Siluridae (Pollard).
I n Polypterus it fuses with th e premaxillary to form an infranasal process of th a t bone.
7. In Macrodon there is a bone, called by Sagemehl the accessory palatine, th a t is apparently
developed in the maxillary breathing valve of th e fish, and th a t is accordingly th e homologue of the
so-called vomer of Polypterus. I t has never been recognised in any other teleost.
8. The palato-quadrate articulations with the ethmoid region of the skull differ considerably
in different ones of the mail-cheeked fishes examined. In Scorpaena and Sebastes there are two of
these articulations, one with an anterior palatine process of the ethmoid cartilage and th e other with
th e ectethmoid; th e lachrymal also articulating with the la tte r bone. In Gottus th e articulation
with the ectethmoid is suppressed, th e palatine there being bound to the lachrymal and th a t bone
alone articulating with th e ectethmoid. In Trigla, this posterior articulation, with the ectethmoid,
is much as in Cottus, while the anterior articulation, with the ethmoid cartilage, has been largely
replaced by a swinging articulation (or attachment) of the lachrymal and palatine with the anterolateral
corner of the nasal bone. In Dactylopterus this la tte r articulation is still more pronounced.
9. The quadrate has, in most if n ot in all teleosts, a posterior process which forms the posterior
boundary of the symplectic groove on th e internal surface of the bone and has supporting relations
with the preopercular. This process of the quadrate is not found, as a p a rt of th a t bone, in th e bony
ganoids, b u t it is elsewhere represented both in Amia and Lepidosteus. l a Amia it has fused with
the symplectic to form a process of th a t bone th a t gives a supplementary articulation to the m andible;
while in Lepidosteus it is the independent, so-called preoperculum of Parker’s descriptions (interoper-
culum, Collinge), which, in th a t fish, has an independent articulation with the quadrate. In the
Muraenidae, th e process and the symplectic seem to both be indistinguishably fused with the body
of the quadrate.