seem as if it might be p a rtly of perichondrial origin, this perichondrial portion of th e bone lying directly
upon the underlying cartilage b u t n o t y e t having acquired endosteal relations to it. In certain specimens.
as seen in Figure 10, a b it of cartilage is enclosed in th e vomer, near its anterior end, this
seeming to indicate th a t this p a rt of th e bone is of perichondrial origin and has surrounded and isolated
a b it of th e chondrocranium. In sections of young specimens th e ascending processes of the
bone lie closely against th e cartilage b u t are separated from it by a line of tissue, and this tissue is
certainly not a simple perichondrial membrane. J u s t what it is, I have n o t sufficient histological
experience to determine, b u t th e bone, if b y origin a purely membrane one, is certainly here in process
of acquiring th a t direct perichondrial contact with th e underlying cartilage th a t Schleip (’04, p. 351)}
describes in 29 mm larvae of Sa lu te B ut there is in Scorpaena, even in th e adult, no indication of
th a t calcification of th e cartilage found in Salmo. I t can, however, be positively asserted th a t the
dorsal limb of th e vomer, n o t only of Scorpaena b u t probably also of all other fishes m which it is
developed, has, or may acquire quite different relations to th e underlying cartilage th a n th a t p a rt
of th e bone th a t lies upon th e v entral surface of the cartilage and is developed in th e mucous m embrane
of th e mouth. And this apparently different origin and character of these two pa rts of the bone is
of importance in th e homologies th a t I shall now seek to establish.
Beginning with Scomber, th e two sto u t condylar processes of th e head of th e voiner of th a t
fish are evidently th e homologues of th e ascending processes of th e vomer of Scorpaena, th e external
surface: of th e processes of Scomber being presented laterally forward and b u t slightly upward (Allis,
’03, p. 68), while in Scorpaena i t is presented dorsally; and in Scomber, as in Scorpaena, these processes
of the bone seem to be in process of acquiring primary relations with th e underlying cartilage.
The cartilaginous interspace of the intemasal ridge-of Scorpaena, p a rtly enclosed as i t is between
th e two ascending processes of th e vomer, is thus th e homologue of the b eak of my descriptions of; the
chondrocranium of Scomber, and hence of a p a rt of th e prenasal process of th e chondrocranium of Amia.
In Amia, th e so-called posterior process of th e premaxillary is, as will be la te r shown, th e probable
homologue of th e articular process, to be later described, of th e premaxillary of Soorpaena.
I t lies directly upon the dorsal surface of th e anterior end of th e chondrocranium, and also upon
the dorsal surface of th e preethmoid (septomaxillary) bone (Allis, ’98); and th e anterior, or proximal
end of th e maxillary articulates with its ventral surface, and also with th e anterior edge of th e preethmoid.
The vomer lies immediately ventral to th e articular end of th e maxillary, and, immediately
posterior to th a t bone, against the ventral surface of th e preethmoid. The lateral edge of th e preethmoid
encroaches upon th e anterior end of the single palatine articular ridge of th e ethmoid cartilage,
and supports, ra th e r th a n forms p a rt of, th a t ridge. Taking all these facts into consideration, it is
evident th a t th e preethmoid of Amia replaces functionally the ascending process of th e h ead of the
vomer of Scorpaena, and th a t if it were to fuse, in Amia, with th e underlying vomer, and th e vomers
of opposite sides were to fuse with each other, a bone functionally th e equivalent of th e vomer of
Scorpaena would arise. B ut the preethmoid of Amia is a perichondrial bone th a t has acquired endosteal
relations to th e underlying cartilage, while th e ascending processes of th e vomer of Scorpaena
are .either purely membrane bones th a t seem to be in process of acquiring perichondrial relations
to th e underlying cartilage, o t are, perhaps, pa rtly of perichondrial bone th a t has n o t y e t acquired
endosteal relations to th e related cartilage. This difference in th e character of the bone m th e two
fishes may however simply indicate th a t th e primary bones develop in a somewhat different manner
in Amia and teleosts, being perhaps formed, in Amia, by direct ossification of the cartilage, while in
teleosts th e cartilage is usually first broken down and then replaced by bone developed in relation to
perichondrial plates. Be this as it may, th e preethmoid of Amia and th e ascending processes of the
vomer of teleosts seem to be developed in relation to th e same region of th e chondrocranium, and
this seems sufficient to establish an homology.
In Esox, th e preethmoid, bone 3 of H uxley’s (’72) descriptions, is an ossification of the posterior
edge of th a t abruptly widened portion of th e anterior end of the ethmoid cartilage th a t Swinnerton
( 02) calls the preethmoid cornu. This ossification, in young specimens of Esox, I find formed of two
th in plates of perichondrial bone, united by a thick outer edge of similar appearance, the two plates
lying one on th e dorsal and th e other on th e ventral surface of the chondrocranium. In older specimens
ossification extends into the cartilage, beween the two plates, from th e outer thickened edge
of th e bone. A lateral corner of the anterior end of bone 2 of H uxley’s descriptions lies directly upon
the dorsal surface of th e preethmoid; and on th e free, latero-posterior edge of the preethmoid there
is a longitudinal articular head, capped with fibro-cartilage, which articulates with a facet on the
mesial surface of th e anterior end of the palatine. The maxillary bone articulates, by a condylar
surface near its anterior end, with a facet on th e anterior end of the palatine, the pointed anterior
end of the maxillary v ery nearly, b u t n o t quite, reaching th e preethmoid and being bound to th a t bone
by tough fibrous tissue. The lateral corner of the anterior end of th e single median vomer rests upon
th e ventral surface of the preethmoid. The preethmoid of Esox, which seems unquestionably the
homologue of th e preethmoid of Amia, thus has relations to th e other bones th a t are in accord w ith
th e supposition th a t i t finds its homologue in the ascending process of the vomer of Scorpaena,
and its manner of development seems intermediate between th a t of the bone of Amia and th a t of
Scorpaena. The vomer of Esox, as is proper where th e preethmoid is an independent bone, consists
of a ventral plate only, as in Amia, without a vestige of a dorsal limb.
The only other fishes in which a preethmoid has been described, so far as I can find, are certain
of th e Cyprinidae, and Belone acus. In the Cyprinidae, Sagemehl (’91) shows a preethmoid (septomaxillary)
lying on either side of the anterior end of th e internasal ridge, and forming p a rt of the
dorsal surface of th e anterior end of the snout. Antero-ventrally it closely approaches the anterior
end of th e vomer, th a t bone having no dorsal limb. The preethmoids (septomaxillaries) are said
(1. c., p. 510) to each lie upon, or in, a cartilaginous process th a t gives articulation n o t only to the
palatine b u t also, through th e intermediation of a pad of cartilage, to the maxillary. A fusion of the
preethmoids with th e vomer would thus certainly here produce the vomer of Scorpaena.
In the Characinidae th e preethmoids are replaced topographically, as well as functionally,
by processes of the mesethmoid (Sagemehl, ’84b, p. 30), the vomer reaching, on either side, the base
of this process, or even forming p a rt of it. The vomer is said to have acquired pronounced primary
relations to th e skull, and, in Erythrinus, to even form an important p a rt of the internasal septum.
The descriptions and figures are however not definite, and it is impossible to tell whether th e preethmoids
are absent or have been absorbed by th e mesethmoid or by the vomer.
In Belone acus, Swinnerton (’02) says there is a preethmoid, and he shows it apparently lying
on the dorsal surface of the snout, slightly antero-mesial to his prepalatine articular facet and close
to th e lateral edge of th e mesethmoid. Having several specimens of this fish, I have looked for this
bone in three of them, b u t I have wholly failed to find it.
The frontal, in Belone, has a long, thin, anterior prolongation which lies closely upon the dorsal
surface of the cartilage of th e snout, exactly as a similar process of the frontal does in Esox. The