and backward in a deep groove th a t lies on th e orbital surface of the prootic and th a t leads into a
large trigemino-facialis chamber. This groove, in Lepidosteus, transmits th e ramus palatinus
facialis as well as the external carotid' a rtery,-the nerve traversing th e foramen in the prootic with
th e artery, and entering th e carotid canal. This foramen in th e prootic of Lepidosteus is accordingly
th e homologue of the palatinus and external carotid foramina of Amia, coalesced into a single opening.
I t has closely th e position of th e palatinus foramen of Amia, and neither it nor th e carotid foramen
are shown by Parker in. any of his figures.
In sections of embryos, a delicate pharyngeal branch of th e glossopharyngeus is found accompanying
th e common carotid artery, and although i t could not be traced as far as th e carotid foramen,
i t doubtless traverses th a t foramen, with th e artery, as in Amia.
The internal carotid artery, having separated from the external carotid immediately beneath
th e palatinus foramen, runs forward in a canal between the cartilage of the basis cranii and th e underlying
parasphenoid, lying in a slight groove on th e dorsal surface of th e la tte r bone. I t is accompanied,
in this canal, by the ramus palatinus facialis and probably also by th e delicate branch of the
glossopharyngeus ju s t above described. Having arrived near th e anterior edge of th e ascending
process of th e parasphenoid, and there lying anterior to th e p itu ita ry fossa, the internal carotid
receives th e efferent pseudobranchial artery. I t then, in all my embryos, immediately separates
into two parts. In th e smaller embryos, these two parts b o th tu rn upward and traverse th e inter-
trabecular space, while in the older embryos, they perforate th e overlying cartilage and so enter
th e cranial cavity, one p a rt traversing a large foramen and th e other traversing a small and imperfectly
enclosed branch canal which leads from th a t foramen. The larger one of these two branches
gives off several intracranial branches and th en leaves th e cranial cavity with th e nervus opticus.
The smaller branch also issues with th e opticus, b u t it gives off no perceptible branches during its
intracranial course, and it may perhaps be reminiscent of th e otherwise wholly wanting anterior
continuation of the efferent pseudobranchial artery. Shortly before th e anastomosis with the efferent
pseudobranchial artery, the internal carotid gives off a small branch which runs forward, accompanying
the palatinus facialis, in an anterior prolongation of, th e canal between th e parasphenoid and the
overlying cartilage of th e base of th e skull. This la tte r a rte ry and the two carotids are all three briefly
mentioned by Wright (’85) in his description of th e arterial circulation in embryos of Lepidosteus,
b u t their foramina and their courses relative to th e cranium are n o t well or sufficiently given by him.
In th e adult, th e trabeculae of opposite sides have fused with each other in the middle
line, and th e internal carotids traverse foramina in th e basis cranii, these foramina corresponding to
th e internal carotid canals of m y descriptions of Amia (’97). Slightly anterior to these canals there is
a shallow transverse groove across th e dorsal surface of the fused trabeculae, this groove corresponding
exactly, in position, to th e canalis transversus of my descriptions of Amia, and being quite undoubtedly
-the homologue of th a t canal. The groove is, however, n o t th e homologue of th e canalis tra n s versus
of selachians, as I have pointed out in a later work (’01), and the selection of the name, in my
descriptions of Amia, was unfortunate. The groove, in Lepidosteus, forms th e anterior boundary
of a slightly raised portion of th e cartilage of th e basis cranii, which extends backward to the anterior
edge of th e p itu ita ry fossa and is th e homologue of th e m uch more pronounced transverse prepituitary
bolster of Amia.
The pseudobranchial artery, in Amia, does n o t itself fuse with the internal carotid, a small
communicating branch, only, which perforates a lateral projection of th e basis cranii, uniting the
two arteries. In Lepidosteus, it is the main efferent pseudobranchial artery, itself, th a t here unites
with the internal carotid, traversing, to reach th a t artery, th e imperfectly closed foramen in thé
anterior edge of th e ascending process of the parasphenoid. This difference in this artery, in these
two fishes, is doubtless due to th e absence of a choroid gland in Lepidosteus ; th a t orbital continuation
of the arte ry th a t supplies th a t gland in Amia naturally being suppressed with th e gland, in Lepidosteus,
and th e communicating branch of Amia becoming, in Lepidosteus, th e direct anterior continuation
of th e main artery.
The palUtinus facialis and external carotid of Lepidosteus run upward and backward, as
already stated, in a groove th a t leads into a trigemino-facialis chamber in th e proötic. This chamber
has a very large trigeminus, and a smaller facialis opening, and its bony mesial wall is a direct posterior
continuation of th e bony wall th a t encloses the anterior p a rt of the cranial cavity; Lepidosteus, in
this, resembling Scomber and th e mail-cheeked fishes, and differing markedly from Amia. The mesial
wall of the chamber is perforated by a single large foramen for the roots of the trigemino-facialis
nerves, two small processes representing th e beginnings of a separation of th e foramen into two or more
parts. Slightly antero-ventral to this foramen th e anterior edge of the proötic is perforated by another
foramen, th e anterior border of which is formed by a small flat b a r of cartilage which, rising from
th e trabecular cartilage and extending upward to th e ventral edge of the alisphenoid, separates, the
foramen from th e ventral portion of the optic fenestra. This foramen transmits th e pitu ita ry vein,
which vein arises beneath the hypophysis, in direct communication with its fellow of th e opposite
side, and from there runs dorso-antero-laterally to traverse its foramen and fall into th e (internal ?)
jugular slightly posterior to th e point where th a t vein is joined by th e orbito-nasal vein. The pituita
ry vein receives a small branch, on either side, from the cross-canal of Sagemehl’s descriptions,
these branches being traced in sections and not in the adult. The vein, in th e adult, lies, in its in tra cranial
course, beneath a mass of fa tty tissue which covers the floor of th e cranial cavity, and this
f a tty tissue in th e cranial c avity of the skull of fishes is said by Sagemehl (’84a) to he between inner and
outer limiting membranes which are p a rts of the dura m ater. Some p a rt of this tissue, in Lepidosteus,
is accordingly the homologue of the tough glistening m embrane th a t, in Amia, forms not only the roof
of the anterior portion of th e myodome, b u t also the mesial wall of the trigemino-facialis chamber
of th a t fish. The foramen th a t transmits th e pitu ita ry vein, in Lepidosteus, is thus quite certainly
th e equivalent of some p a rt of the ventral portion of the orbital opening of th e myodome of Amia.
Immediately dorsal to the foramen for the pituitary vein, between the adjoining edges of the
proötic and alisphenoid, there is another foramen, which transmits the nervus oeulomotorius and
probably the radix profundi also, for although this latter nerve, in my 80 mm specimen, pierces the
cartilaginous cranial wall close to but wholly separate from the oeulomotorius, I do not find a separate
foramen in the one adult skull th a t I have examined in this connection. Van Wijhe (’82) says that
he found the profundus issuing by a separate and independent foramen. Somewhat dorsal to these
two foramina, in the sections of my 80 mm specimen, the trochlearis pierces the cranial wall, and,
slightly posterior to that nerve, the wall is perforated by a branch of the orbito-nasal vein. These
two latter foramina are, one or both, represented, in my adult specimen, in a short canal th a t tía-
verses the. alisphenoid slightly dorsal to the oeulomotorius foramen.
Stannius (’49, p. 19) says that, according to Müller, the oeulomotorius, trochlearis and trige-:
minus of-Lepidosteus all issue through a single large foramen in the „Keilbeinflügel” ; a statement
th a t is certainly not whollÿ correct.