th e la tte r nerve being accompanied by certain meningeal vessels. The foramen rotundum is said by
Thane (Quain, vol. II , p t. I) to have been separated off from th e sphenoidal fissure by th e growth
of bone around th e nerve, the foramen ovale being similarly cu t off from the foramen lacerum. The
foramen lacerum is an aperture between th e apex of th e petrous portion of th e temporal bone and
th e body and great wing of the sphenoid, and would seem to correspond to the trigeminus foramen
of Amia, th o u g h .it may include some p a rt also of th e trigeminus opening of the trigemino-facialis
chamber of teleosts. Comparison with fishes would thus indicate th a t th e foramen ovale and th e
foramen rotundum must both be pa rts of the foramen lacerum, instead of being respectively parts
of th a t foramen and of th e sphenoidal fissure. The foramen spinosum of man, which perforates the
great wing of the sphenoid and transmits the large middle meningeal vessels, must have its homologue
in one or both of those perforations of the alisphenoid th a t, in teleosts, transmits branches of th e
external carotid arte ry and orbito-nasal vein.
The foramina related to the nervus facialis are n o t so readily homologized. The facialis foramen
and th e facialis opening of th e trigemino-facialis chamber of teleosts must together represent parts
of the Aqueduct of Fallopius of man, b u t apparently not th e whole of it, for th e lower p a rt of the
aqueduct is said by Thane to be included between th e outer surface of th e periotic and the tympanic
plate, and until this la tte r plate is identified in fishes, th e homologue of the stylo-mastoid foramen
can not be determined. The hiatus Fallopii, which leads from th e Aqueduct of Fallopius to the
depression on th e petrous th a t lodges th e Gasserian ganglion, is evidently th a t p a rt of the trigemino-
facialis chamber th a t lies between the facialis and trigeminus foramina; th e Vidian canal being what
I have described as the palatine canal in Amia, a canal th a t lies between th e parasphenoid (pterygoid
of man, Gaupp, ’05) and the cartilaginous basis cranii of th a t fish. In teleosts this canal is absent
because of th e suppression of th e cartilage in this region. The internal jugular vein does not, in man,
issue with th e nervus facialis, issuing instead through th e jugular foramen which transmits also the
glossopharyngeus, vagus and spinal accessory nerves. The internal carotid canal, which, in man,
traverses th e petrous p a rt of the temporal bone, seems n o t to be the exact homologue of th e internal
carotid foramen of fishes, this la tte r foramen lying between the prootic and parasphenoid instead of
traversing the former bone. B ut as th e a rte ry th en traverses th e cavernous sinus in man and th e myo-
dome in fishes th e canal of th e one must be in large p a rt th e homologue of th e foramen of the other.
Regarding the bones of th e region, th e posterior .clinoid wall is represented in the mesial processes
of th e prootics of Amia, the anterior clinoid wall being represented either by the basisphenoid
of teleosts, by the prepituitary p a rt of th e mesial processes of th e prootics, or by those bones fused
to form a single element. The spicula of bone th a t, in man, sometimes unite th e anterior and posterior
clinoid processes are then those pa rts of the mesial processes of the prootics of teleosts th a t lie lateral
to th e p itu ita ry opening. The parasphenoid leg of th e alisphenoid of teleosts is the great wing of
th e sphenoid bone of man, the basisphenoid leg of th e bone of fishes apparently being suppressed
by an invading growth of th e orbitosphenoid which forms th e small wing of the sphenoid of man.
The basisphenoid of fishes, if it persists as a separate bone, is the presphenoid of man, b u t, as just
above stated, th a t bone of man would seem to a t least include th e prepituitary pa rts of th e mesial
processes of the prootics of teleosts. The basisphenoid of man, if it is found in fishes, would seem to
be represented in a p a rt of th e prootic, b u t it is perhaps possible th a t th e median ossification in the
dorsal surface of th e prootic bridge of my one specimen of Gadus morrhua, described below, may
be th e homologue of th a t bone.
Swinnerton, it should here be stated, has arrived, in a study of the development of Gasteros-
teus, a t conclusions quite different from those just above proposed, in so far as regards the position
of the myodome relative to th e cranial walls in fishes, and th e homologies of the hypophysial fenestra.
According to him (’02, p. 527) those p a rts of the parachordals th a t, in embryos of Gasterosteus, bound
laterally the interparachordal fossa, become depressed in late embryonic stages, so as to appear as
mere downward processes of th e prootics. These processes are said to be capped with cartilage>>to
each be continued posteriorly by a ridge on th e ventral surface of th e posterior portion of the related
prootic, and, posterior to th a t bone, by a similar ridge on the ventral surface of the basioccipital.
The two processes are said to enclose between themselves the anterior portion of the myodome, which
portion is said to accordingly be an actual derivative of th e cranial cavity; while the two ridges th a t
form posterior continuations of th e processes enclose a posterior portion of th e myodome, which
is said to be extracranial in position. These conclusions lead Swinnerton to th e further conclusion
(1. c,, p . 528) th a t th e so-called hypophysial fenestra of th e skull of adult teleosts is related to the
parachordals, alone, and hence can not be th e homologue of the pitu ita ry (hypophysial) fossa of
embryos, which fossa is related to the hind ends of the trabeculae. The so-called hypophysial fenestra
of th e adult fish can n o t then be th e homologue of th e hypophysial (pituitary) fenestra of higher
animals, and Swinnerton accordingly proposes for this fenestra of the ad u lt teleost the name inter-
parachordal fossa. The position, in th e adult, of th e p itu ita ry fossa of embryos, Swinnerton does
not give; th e inference being th a t it has wholly disappeared in th a t suppression of the hind ends of
the trabeculae th a t is said to tak e place in late embryonic stages.1)
Those teleosts in which the myodome is said to be absent can now be considered. Vrolik
( 73) says th a t it is absent in all the Gadidae, and also inSilurus, Lophius and the eel; Gill says (’91b,
p. 363) th a t it is absent in the Cyclopteroidea, and also (’82) in Echeneis; Swinnerton (’02, p. 576)
says th a t it is absent in Fistularia and Syngnathus; and Jordan and Evermann (’98) say th a t the
basis cranii is simple in the Hemibranchii and Lophobranchii, which include Fistularia and Syngnathus;
Cope (quoted by Gill, ’88, p. 576) says that it is absent in all the fishes of the group Scypho-
branchii, which group (Cope, ’71) includes the Uranoscopidae, Gobiidae, Blenniidae, Gobiesocidae
and Cottidae; Gierse (’04) says th a t it is wholly wanting in Cyclothone; and Starks (’05 a) says that
it is absent in Caularchus, Callionymus and the Batrachididae, confirming also its absence in the
Gobiesocidae. McMurrich (’84) says th a t it is rudimentary in Ameiurus; and Sagemehl (’91, p. 574)
says th a t it has undergone retrogression in Cobitis, Misgurnus, Nemachilus and Acanthophthalmus.
Boulenger (’04) says th a t the basis cranii is simple in the Mormyridae, Osteoglossidae, Pantodontidae,
Phractolaemidae, Stomiatidae, Gonorhynchidae, Cromeriidae, Galaxiidae, Gobiiformes, Discocephali,
Comephoriidae, Rhamphocottidae, and in all the five families of his suborder Pediculati. He further
says th a t the basis cranii is double in the symmetrical forms of his division I of the suborder Acantho-
pterygii; which would seem to imply th a t it is simple in the asymmetrical forms of the same division,
that is the Pleuronectidae. And the expression „basis cranii simple“, while it is, strictly speaking,
descriptive of a condition of the bony skull alone, is currently considered as equivalent to saying
*) Gaupp, in Bd. 3 of Hertwig’s Handbuch der vergleichenden und experimentellen Entwickelungslehre der Wirbel
tiere, a work that I have only seen since this manuscript was sent to press, describes practically similar conditions
Salmo, and arrives at practically similar conclusions regarding the homologies of the parts. This would seem to establish
the fact that the basi-occipital portion of the myodome is extracranial in origin. Regarding the prootic portion of the
myodome, Gaupp’s descriptions, would seem to confirm my contention that it is an intramural space and not an intracranial
one.