The so-called quadrates of osseous fishes are thus n o t all equivalent structures. The articulations
of the mandible with th e suspensorial apparatus are also not all similar; Amia being th e one
known exception to th e otherwise general rule, b u t L epidosteus somewhat resembling it. A further
development of th e conditions found in Amia might transfer th e mandibular articulation from the
palato-quadrate to the hyomandibular.
10. On th e hind edge of th e metapterygoid, in all of the mail-cheeked fishes examined excepting
Cottus and Dactylopterus, there are two flanges, apparently of membrane (exosteal) origin,
one of which is lateral and th e other mesial in position. Between these two flanges th e external
carotid arte ry runs downward to fall into th e arteria hyoidea shortly before th a t a rte ry joins th e
opercular hemibranch, and afte r it' has passed from th e external to th e internal surface of the
palato-quadrate apparatus. On th e opposing surfaces of th e two flanges th e lavator arcus palatini
muscle has th e larger p a rt of its surface of insertion.
In Cottus and Dactylopterus these two flanges, instead of being one lateral and th e other
mesial, are respectively one ventral and the other dorsal; both flanges lying in the plane of the
body of the metapterygoid, with their adjoining edges fused b u t perforated by a foramen which
transmits th e external carotid and represents th e V-shaped space between the flanges in th e other
fishes. In these two fishes th e flanges appear to be of endosteal ra th e r th a n of exosteal origin.
In Amia th e lateral one of these two flanges is represented in th e so-called metapterygoid
process of th e metapterygoid, th e mesial flange being represented in th a t p a rt of th e body of the
metapterygoid th a t lies posterior to the process. In Amia both these pa rts of the bone are quite
evidently of endosteal origin.
11. In all of th e mail-cheeked fishes examined there is a vessel, apparently an artery, th a t
arises in connection with what seem to be either glomuses or rudimentary glandular structures
related to the efferent arteries of th e first three branchial arches. Certain evident connections of
these glomuses with th e lymphatic vessels were found, and occasional apparent connections with
th e arteries, b u t no indication whatever of a connection with th e venous system. The vessel
parallels th e common carotid and its branches, and peripherally th e walls of th e branches of the
vessel change abruptly in character, and there appear as lymphatic spaces. The fact th a t th e
external carotid branch of the vessel traverses th e trigemino-facialis chamber in much the position
of th e hyo-opercularis arte ry of Amia, led me a t first to homologize the vessel with th a t artery,
b u t as there is much doubt of th e correctness of this homologization 1 have described th e vessel as
the vessel x. In Dactylopterus one branch of the vessel seemed to enter th e opercular hemibranch. In
Polyodon the system is much more developed th an in the mail-cheeked fishes, and I am investigating
it in th a t fish. I t would seem as if th e glomuses from which th e vessel arises might be serial
homologues of certain of the nephritic structures, and possibly also homologues of th e so-called
thymus of Polypterus.
12. The external carotid, in all th e fishes examined, traverses th e trigemino-facialis chamber,
gives off several branches, and then terminates in a branch which tu rn s downward between two
flanges on th e hind edge of th e metapterygoid and falls into the arteria hyoidea shortly before th a t
a rte ry enters th e opercular hemibranch. This terminal portion of the external carotid corresponds
closely in position to, and is probably the homologue of th e secondary afferent pseud obranchial arte ry
of my descriptions of Amia, and its connection with th e arteria hyoidea, instead of with the
pseudobranch, would give origin to th e teleostean arrangement.
13. The alisphenoid is perforated, in Scorpaena, Trigla and Lepidotrigla, by a foramen which
transmits delicate branches of th e external carotid arte ry and the vessel x, these branches being
accompanied by a nerve which is composed of the lateralis fibers destined to innervate the terminal
organ of the supraorbital canal and of certain other general cutaneous or communis fibers. In D actylopterus,
th e nerve th a t traverses the foramen does n o t contain lateralis fibers; the nerve destined to
supply the terminal organ of th e supraorbital canal there having an extracranial course. The alisphenoid
is also perforated, or notched, in Scorpaena, Trigla and Lepidotrigla by another foramen,
which transmits th e homologue of th e anterior cerebral vein of my descriptions of Amia. These
foramina, one or both, are found in the other mail-cheeked fishes also, b u t the arteries and veins
th a t traverse them were not there traced.
14. The parietal is fused, in all th e mail-cheeked fishes examined, with a mesial extrascapular
latero-sensory element to form a single bone, which I have called the parieto-extra-
scapular. This same fusion of these two bones is also found in the Characinidae and Cyprinidae
(Allis ’04) and has been definitely established in no other fishes th a t I know of, excepting Chanos.
15. The side walls and floor of the skull of osseous fishes are more or less completely double
in th e sphenoid (orbito-temporal, Gaupp) and labyrinth regions; these walls being there represented
in varying proportions by membrane, cartilage or bone. Between the two walls, in the sphenoid
region, lies the myodome with its upper lateral or trigemino-facialis chambers, while between the two
walls in the labyrinth region lie the membranous ears. The myodome and its trigemino-facialis
chambers are thus all intramural spaces. The floor of the myodome proper is perforated by the
hypophysial fenestra, while its roof is perforated by the pitu ita ry opening. These two perforations
of the cranial floor are : doubtless strictly homologous in all vertebrates, b u t it must be determined,
in each case, which one of the two perforations is in question. The myodome proper lodges a cross-
commissure of the pitu ita ry veins, and is the probable homologue of the cavernous and intercavernous
sinuses of the human skull. The postpitui-tary portion of its roof apparently always chondrifies,
and is the postclinoid wall. The prepituitary portion of its roof does not usually chondrify (Argyro-
pelecus m ay be an exception), and it and the basisphenoid, one or both, represent the anterior clinoid
wall. The orbital opening of the myodome, on either side, is the sphenoidal fissure.
The trigemino-facialis chamber of either side is, in the mail-cheeked fishes, and probably
in most other teleosts, separated from the myodome by a p a r titio n of bone. I t lodges the trigeminus
and related sympathetic ganglia, and is the homologue of the cavum Meckelii of th e human skull.
Its outer wall is, in all the mail-cheeked fishes examined, excepting Cottus, represented by a narrow
bridge of bone, this wall of th e chamber here forming the outer surface of the skull. In Cottus this
outer wall is entirely of membrane, the inner wall of the chamber thus here forming the outer surface
of the prepared skull. The internal wall of the chamber forms p a rt of the bounding walls of a recess
on the internal surface of the skull, and this recess lodges the lateralis and communis portions of the
V V II ganglionic complex. In Amia these portions of the ganglionic complex He in the upper lateral
chamber of the myodome. There is accordingly question as to whether the inner wall of the chamber
of teleosts corresponds exactly to the same wall in Amia. In any event, the recess th a t lodges, in
teleosts, the lateralis and communis ganglia would seem to be the homologue of some p a rt of the
aqueduct of Fallopius.
The trigemino-facialis chamber is continued anteriorly by an intramural space th a t lodges the
jugular vein and the truncus ciharis profundi. The outer wall of this space is largely of membrane in