to be th e homologue of th e transverse prepituitary bolster of Amia. The lateral edge of the plate,
in Lacerta, is connected, on either side, by the pila metoptica, with th e taenia parietalis media, this
la tte r structure being a horizontal b a r of cartilage th a t forms p a rt of the side wall of th e cranial cavity.
The pila metoptica forms p a rt of the anterior boundary of th e fenestra metoptica, which transmits
the oculomotorius and trochlearis nerves; those nerves th u s undoubtedly running forward lateral
to th e pila metoptica, into the orbit. The cartilaginous pila metoptica of Lacerta thus corresponds,
in its relations to these two nerves, to th e basisphenoid leg of th e alisphenoid bone of Lepidosteus,
and to th e fibrous tissue th a t, in Amia, represent th e same leg and forms th e mesial boundary of the
ta ll orbitail opening of th e myodome. In Amia, th e relations of th e two nerves to the basisphenoid
leg of th e alisphenoid are n o t positively indicated, th a t leg being represented by an undefined
portion of a continuous membrane. In teleosts, th e oculomotorius issues, in all th e fishes I have
examined, posterior to th e sutural connection of the alisphenoid with th e basisphenoid, and
hence lies posterior to th e basisphenoid leg of th e alisphenoid. The trochlearis has however
in teleosts th e same indefinite relations to the basisphenoid leg of th e alisphenoid th a t it has
in Amia, for it issues along th e ventral or ventro-anterior edge of th e alisphenoid, b u t anterior
to th e sutural connection of th a t bone with th e basisphenoid. I t must accordingly either lie
anterior to th e basisphenoid leg of the bone, or perforate an unossified portion of th a t leg; probably
th e latter.
In Lacerta th e hypophysis lies posterior to th e subiculum infundibuli, between it and the
crista sellaris. Lateral to th e crista sellaris, the nervus abducens pierces th e basal parachordal plate,
near its anterior edge, and, running forward in th e plate, opens on its very edge; th e foramen not
being shown in ventral views. From there th e nerve must run forward dorsal to th e trabeculae,
as it does in the Frog (Gaupp, ’93a) and Necturus (Platt, ’97), and in this p a rt of its course it must
lie between the trabeculae and an overlying membrane of some kind, doubtless a somewhat differentiated
layer of the dura mater. This membrane would certainly underlie th e hypophysis and so
represent a membranous floor of this p a rt of th e cranial cavity, b u t to what extent it is developed
or differentiated, I can not determine from the literature a t my disposal. Assume it to be well developed.
I t would extend between th e subiculum infundibuli and th e crista sellaris, forming a membranous
fossa around the hypophysis, and leaving a space between itself and th e underlying cartilage
of th e skull. This space must be traversed by th e vein th a t is said by Gaupp (’93b, p. 571) to run
forward from th e hypophysis into th e orbit, and which is th e evident homologue of th e pitu ita ry
vein of my descriptions of Amia, Lepidosteus and Scorpaena. The space must, furthermore, be
traversed by th e carotid artery, which artery having either traversed th e hypophysial fenestra or
a closely adjoining and independent foramen, is said by Gaupp (1. c; p. 571) to run forward close
to th e b ra in; th u s doubtless passing dorsal to th e subiculum infundibuli. These conditions in Lacerta
are th u s all too similar to those in th e fishes referred to not to warrant th e following conclusions;
(1) th a t th e cartilaginous floor of th e cranial cavity of Lacerta is probably th e homologue of the
ventral floor of th e myodome of fishes; (2) th a t there is, in th e p itu ita ry region of this skull, and
dorsal to th e cartilaginous floor, a space of uncertain dimensions which corresponds to a p a rt, if n o t
to th e whole, of the myodome of fishes; (3) th a t th e hypophysial fenestra of Lacerta is consequently
th e strict homologue of the hypophysial fenestra of Lepidosteus; and (4) th a t th e subiculum infundibuli
is the homologue of th e basisphenoid cartilage of Scorpaena, and hence of th e transverse prep
itu ita ry bolster of Amia.
With th e human skull I have already attempted, in an earlier work (’97b), to compare the
condition found in Amia, and certain conclusions there arrived a t can be repeated here with additional
facts in their support.
In Man (Qùain ’92/96), the Gasserian ganglion lies in the cavum Meckelii, th a t cavum being said
to be a recess in the dura mater which occupies a depression on the upper surface of the petrous
portion of th e temporal bone. B ut this so-called recess must be a space in the dura mater and not
a simple recess on its cerebral surface; for elsewhere in th e same work th e Gasserian ganglion is said
to lie between th e inner and outer layers of the dura, the inner one of these two layers being the
primitive, single-layered dura, and the outer one being th e endocranium, or internal periosteal membrane
of th e skull. The fusion of these two separate membranes of embryos is said to form the doublelayered
dura of th e adult, the Gasserian ganglion being, in this process, enclosed between the two
layers. The internal p a rt of th e cavum Meckelii is said to come into close relations with the posterior
extremity of th e cavernous sinus, th a t sinus also being a space between the two layers of the dura
of th e adult, and the sinuses of opposite sides being in communication b y means of the intercavernous
sinuses. Between the cavernous sinuses of opposite sides, in a median depression on th e dorsal surface
of th e dura, lies th è pitu ita ry body. The cavernous sinuses each receive the ophthalmic vein
anteriorly, these veins communicating with each other across th e middle line by means of th e inte rcavernous
sinuses, and discharging their blood posteriorly into the petrosal sinuses. The intercommunicating
veins are accordingly th e homologues of the pitu ita ry veins of my descriptions of
fishes, and th e cavernous sinuses, intercavernous sinuses, and Cava Meckelii are together th e apparently
stric t homologues of the myodome of Amia; th a t myodome consisting, as I have already explained,
of a ventral portion which is th e homologue of the myodome of teleosts, and an upper lateral
chamber, on either side, which is th e homologue of the trigemino-facialis chamber of teleosts.
The outer wall of each cavernous sinus is traversed b y the oculomotorius, trochlearis and abducens
nerves, by the ophthalmic and superior maxillary branches of the trigeminus, and by the
internal carotid artery. Having traversed th e wall of the sinus, the oculomotorius, trochlearis,
abducens and ophthalmicus trigemini all issue into th e hind p a rt of th e orbit through the sphenoidal
fissure, th a t fissure lying between the great and small wings of the sphenoid bones, the former of
which is said to be formed by th e alisphenoid bone and the la tte r by th e orbitosphenoid. The fissure
is also traversed by the ophthalmic vein as it passes from the orbit into th e cavernous sinus. The
sphenoidal fissure thus corresponds in every detail, excepting in th a t it transmits the ophthalmicus
trigemini, to the orbital opening of th e myodome of Amia. B u t th e fissure lies, in man, between
the alisphenoid and orbitosphenoid bones, instead of between th e parasphenoid and basisphenoid
legs of th e alisphenoid. This however seems unimportant, for, as I have also pointed out (’97b),
th e so-called basisphenoid of Amia is probably simply a p a rt of th e orbitosphenoid, ossifying from
a separate and independent center; the orbitosphenoid of Amia and Man invading a region th a t
is ossified as p a rt of th e alisphenoid in teleosts. Regarding th e ophthalmicus trigemini, which tr a verses
the sphenoidal fissure in man, th a t nerve is th e homologue of th e ophthalmicus profundus
of fishes, a nerve not found in Amia or teleosts, b u t as it arises from the profundus ganglion it would
probably issue from the skull with the ciliaris profundi, which la tte r nerve traverses th e orbital
opening of the myodome.
The foramen rotundum and the foramen ovale both perforate, in man, the great wing of the
sphenoid, and transmit respectively th e superior and inferior maxillary branches of the trigeminus,
Zoologica. Heft 57.