ventral end of each of these ridges projects, as a small process, toward th e dorsal end of th e ascending
process of th e parasphenoid, and is connected by fibrous tissue with th e dorsal end of th a t process,
this tissue bridging, to reach th e parasphenoid, a narrow intervening portion of th e orbital surface
of the prootic. The tissue related to th e antero-mesial ridge is always more strongly developed th an
th a t related to the postero-lateral one, being almost ligamentous in character. In one specimen it
had even become entirely ossified b y invading growths from the alisphenoid and parasphenoid, a
complete bony foramen thus being formed which is th e homologue of th e internal jugular foramen
of Allen’s (’05, p. 81) descriptions of Ophiodon. When th e ligamentous tissue does n o t ossify, and
th a t is th e usual condition in the specimens th a t I have examined, th e foramen becomes an internal
jugular notch. The bottom of this notch, or th e m esial border of the foramen w hen there is a foramen,
is usually, b u t not always marked by a slight ridge on th e prootic; and this ridge, where there is
simply a notch, forms th e dorso-lateral corner of th e orbital opening of th e myodome, and separates
th a t opening from a groove on th e posterior wall of th e orbit. This groove lies on th e orbital surface
of th e prootic, leads dorso-postero-laterally into th e trigeminus opening of th e trigemino-facialis
chamber, and lodges n o t only the internal jugular vein, b u t also th e truncus ciliaris profundi. Because
of th e name given to the foramen (or notch) th a t forms its antero-mesial boundary, the groove
can be called th e internal jugular groove. Coming along this groove, th e truncus ciliaris profundi
passes through the internal jugular notch, mesial to the spanning ligament, and th en turns forward,
in th e orbit; the neTve thus entering th e orbit mesial to, and hence morphologically anterior to, th e
spanning ligament. The oculomotorius traverses a foramen in th e prootic th e external aperture
of which lies immediately antero-mesial to th e internal jugular notch, and then runs forward in the
orbit, thus also lying mesial and hence morphologically anterior to th e band of ligamentous tissue.
The trochlearis has similar relations to th e band of tissue, while th e trigeminus and lateralis nerves
issue, and always lie, lateral, and hence morphologically posterior to it. The band of ligamentous
tissue and th e associated process-like ridge of th e alisphenoid, th u s together correspond exactly,
in their relations to these cranial nerves, to th e pedicle of the alisphenoid of Amia; and if, in Scorpaena,
th e process of th e alisphenoid were alone to be prolonged, by ossification of th e ligament, its
v e n tra l end would rest upon th e ascending process of the parasphenoid, and, interno-posterior to th a t
process, upon a portion of the lateral bounding wall of th e orbital opening of the myodome, exactly
as it does in Amia. The process and band, together, are thus quite certainly th e homologue of the
pedicle of th e alisphenoid of Amia.
Tha t small p a rt of the alisphenoid of Scorpaena th a t lies ventral to its slightly developed
pedicle must then correspond to th a t flange of th e alisphenoid of Amia (Allis, ’97a, fig. II) th a t lies
internal to the well-developed pedicle of the bone of th a t fish. In Amia this flange of th e alisphenoid
gives a ttachment to th e dorsal edge of th e tough membrane th a t, in th a t fish, forms the lateral wall
of the cranial cavity and th e mesial (morphologically anterior) wall of th e tall orbital opening of the
myodome. Ventrally this membrane is closely attached (Allis, ’97a, p.494) to th e dorsal surface of the
transverse cartilaginous prepituitary bolster of th e fish; and in this p a rt of the membrane, or perhaps
pa rtly also in tissues th a t remain after th e resorption of th e cartilaginous bolster, the body and pedicle
of th e T-shaped basisphenoid of teleosts are developed. In both Scomber and Scorpaena the ventral
edge of th e alisphenoid suturates with th e lateral edge of th e body of th e basisphenoid; this showing
th a t a portion of th e membrane th a t forms th e antero-mesial wall of th e orbital opening of the
myodome of Amia is alisphenoid membrane, and potentially a p a rt of th e alisphenoid bone.
The alisphenoid of Amia and teleosts is thus, in principle, an inverted Y-shaped bone, the
anterior arm of the inverted Y resting on the lateral edge of the actual or potential basisphenoid,
and the posterior leg resting on th e lateral and morphologically posterior wall of the orbital opening
of th e myodome, the ascending process of the parasphenoid there coming into supporting relations
with it. The bone thus straddles th e orbital opening of th e myodome, and through the passage between
its legs, in Amia, the oculomotorius, trochlearis, and profundus nerves enter the orbit; the passage
not, however, representing the fused foramina of those nerves (Allis, ’97b), their true foramina being
where they respectively pierce the membrane which, in Amia, forms th e entire lateral bounding w a ll
of this p a rt of th e cranial cavity. All three of th e nerves, in Amia, certainly lie anterior to the parasphenoid
leg of th e alisphenoid; and th e profundus certainly lies posterior to the basisphenoid leg of
th a t bone. What th e relations of th e trochlearis and oculomotorius are to this la tte r leg is not evident,
for there is nothing in th e continuous membrane to in any way indicate th e alisphenoid region. In
teleosts, where, as in Scorpaena, this membrane of Amia may be replaced by bone, the relations of
these two nerves to th e basisphenoid leg of th e alisphenoid are also n o t evident; for although, in my
descriptions of Scomber, I stated th a t, in th a t fish, the trochlearis issued along th e antero-mesial
edge of th e alisphenoid, a reconsideration of the figures makes it evident th a t the so-designated edge
of th e bone is, in reality, p a rt of its ventral edge. These two nerves, in teleosts, thus both seem to
have been pushed downward, by the growing ventral edge of the alisphenoid, and to lie, in the adult,
simply ventral to th a t bone, without positively evident anterior or posterior relations to it.
In Gasterosteus, where, according to Swinnerton, the alisphenoid is wanting, a dorsal prolongation
of th e ascending process of the parasphenoid has invaded the region of the parasphenoid
leg of th e alisphenoid, and there has come into sutural contact with th e closely adjacent ventral
edge of th e ventral process of the frontal. This condition of the parasphenoid is also found in Cottus
octodecimospinosus, and will b e fully described when describing th a t fish. I t is apparently also found
in the Barbidae and Cobitiidae, and in Homaloptera (Sagemehl *91, p. 564).
S P H E N O T I C .
The sphenotic (postfrontal, postorbital ossification) is an irregular bone th a t forms the summit
of the postorbital process of the skull. I t forms p a rt of the inner as well as p a rt of th e outer surface
of the brain case. Its outer surface has lateral, dorsal and anterior regions, separated by sharp angles.
The anterior surface forms p a rt of the hind wall of the orbit. On it there is a relatively large recess,
beneath a th in flange of bone, and from this recess the oticus canal leads upward laterally and backward
in a curved course, traversing th e bone and issuing on its dorsal surface near its hind end. I t
transmits the ramus oticus lateralis, accompanied b y both communis and general cutaneous fibers,
and is the homologue of the similar canal described by me in Scomber. On th e lateral surface of the
bone there is a large articular facet for the anterior head of the hyomandibular, the ventral portion
of th e facet being formed by the prootic. Immediately dorso-anterior to this facet there is a roughened
surface which gives origin to the levator arcus palatini, and immediately dorso-posterior to the
facet there is a depression, open posteriorly, which forms the anterior p a rt of the dilatator fossa.
The dorsal surface of th e bone, which is flat, gives support to th e postfrontal bone and also to the
anterior edge of th e pterotic and the lateral edge of th e posterior portion of the frontal. The internal
surface of th e bone is relatively small, and presents, as in Scomber, two deep recesses separated by
a thin and nearly vertical partition of bone which, projecting backward and mesially into the cranial
Zoologlca. Heft 57. g