side, the rectus externus muscle has its origin. Ventro-anterior to th e rectus externus, and also
wholly on th e membrane, th e rectus internus has its origin. The rectus inferior runs upward and
backward lateral to th e rectus internus, and has its origin in p a rt on th e posterior portion of the
membrane th a t closes th e optic fenestra and in p a rt on th e adjoining and bounding portions of the
interorbital process of the parasphenoid. The rectus superior runs downward posterior to th e rectus
inferior, anterior to the rectus externus, and lateral to th e rectus internus, and has its origin on the
dorsal surface of th e parasphenoid. The pitu ita ry vein forms a transverse commissure across the
dorsal surfaces on th e recti interni, and, on either side, runs dorso-posteriorly to join th e jugular
vein as th a t vein enters th e trigemino-facialis chamber. The internal carotid arte ry traverses a
canal th a t lies wholly in th e parasphenoid, traversing th a t bone from its ventral surface to issue
on th e dorsal surface in th e region of th e ventral perforation of th e interorbital wall. There it gives
off th e orbito-nasal artery, a n d , joining its fellow of the opposite side, passes upward in the
middle line, between th e recti interni and immediately anterior to th e transverse commissure of
th e pitu ita ry veins, and, piercing th e membranous floor of th e cranial cavity, enters th a t cavity.
Immediately anterior to the communicating branch to the internal carotid, the afferent pseudobranchial
a rte ry communicates with its fellow of th e opposite side by a cross-commissural branch which
traverses the ventral perforation of th e interorbital wall.
The ventral perforation of the interorbital wall of Dactylopterus, and some indeterminate
but adjoining portion of the hind end of the orbit, is thus a myodome strictly comparable to that
of the other fishes of the group, but it is so short, antero-posteriorly, th a t it appears transverse
instead of longitudinal in position. In Scorpaena the myodome extends almost to the hind end of
the basioccipital. In Peristedion it has been considerably shortened, and extends, as it does in Amia,
only to the hind edges of the prootics. In Dactylopterus, it has been still further shortened, and,
as a result of this shortening, some portion of the prootic bridge has been tilted upward so th a t it
lies in a nearly vertical transverse position and forms an apparent part of the hind wall of the orbit:
the myodome being, so to speak, squeezed or shoved out of the brain case into the hind end of
the orbit.
The PARASPHENOID is a broad flat bone the principal features of which have ju s t above
been described in describing the orbit. I t suturates anteriorly with the vomer and ectethmoids,
posteriorly with th e basioccipital, and laterally, in its posterior portion, with th e prootics. Dorsally
i t is in sutural contact, by its interorbital process, with th e alisphenoids. Its ascending process,
on either side, is a small pointed process which suturates with th e ventral end of th e sharp angle
th a t separates the lateral and orbital surfaces of th e prootic. On the dorsal surface of th e bone,
between these processes, there is a transverse ridge, already described, and posterior to this ridge
th e dorsal surface of the bone is flat and smooth, without the median longitudinal ridge usually here
found on the bone. This seems to indicate, as will be more fully discussed below, th a t th e transverse
ridge represents the longitudinal ridge usually found in other fishes, b u t here greatly shortened. The
ridge is tall and th in and inclines upward and backward, and on its posterior surface, in the median
line, there is a large pit-like depression. The internal carotid foramina perforate th e bone, instead
of lying between it and th e prootics.
The BASISPHENOID is either wanting or is indistinguishably fused with the interorbital
process of the parasphenoid.
The ALISPHENOID, as seen from the outside of the skull, is a sub-semicircular bone, the
curved edge directed ventrally and deeply notched to form the superior border of the optic fenestra.
Immediately anterior to this fenestra, th e ventral edge of th e bone suturates with the dorsal edge
of the middle region of th e interorbital process of the parasphenoid, while anterior to th a t region of
sutural contact it is in synchondrosis with the cartilage of the interorbital wall. Posterior to the
optic fenestra it suturates with the prootic, th e hind corner of the bone being in synchondrosis with
a small interspace of cartilage th a t lies between it and the prootic and sphenotic. On th e internal
surface of th e bone there is, as in the other fishes of the group, a large brace-like process which
separates the mid-brain and fore-brain recesses of th e cranial cavity. The dorsal edge of this process
is greatly expanded, as is also th e dorsal edge of the bone itself, the large flat surface thus formed
giving support mainly to the frontal; b u t the hind corner of th e brace-like process extends backward
beneath th e anterior edge of th e supraoccipital and so gives support to th a t bone also.
The alisphenoid is perforated, in the adult, immediately posterior to the optic fenestra, by
a small foramen which doubtless transmits th e nervus trochlearis; th a t nerve traversing th e optic
fenestra, close against th e alisphenoid, in 5 cm specimens. Near its dorsal edge the bone is traversed
b y a small canal which transmits a branch of the orbito-nasal vein, accompanied by a general
cutaneous branch from the r. oticus trigemini. The bone is not traversed, as it is in the other fishes,
by the lateralis branch th a t innervates the terminal organ of the supraorbital canal, th a t branch
passing upward external to the alisphenoid and th en perforating the frontal.
The SPHENOTIC is a small and irregular bone and is, in all my specimens, inseparably ankylosed
with the postfrontal, which la tte r bone lies upon and occupies about one half of the dorsal surface
of the sphenotic. The remainder of the dorsal surface of the sphenotic gives support mainly to the
pterotic, a small corner only of the bone supporting the hind edge of the frontal. In the fusion of
th e sphenotic with th e postfrontal, Dactylopterus resembles Polypterus, which la tte r fish is the
only other one in which, as I have s tated in a recent work (’04, p. 56), I know this fusion to be of
regular occurrence. Ridewood, since the publication of th a t work, has said (’04a, p. 56) th a t the
fusion of these two bones is also of almost constant occurrence in Amia, their separation in th a t fish,
being an ,',occasional feature only“ . While this may be tru e of alcoholic or otherwise preserved specimens,
it certainly is not of fresh material.
The sphenotic is in sutural contact with the prootic and pterotic b u t not with th e alisphenoid,
being separated from th e la tte r bone by a small interspace of cartilage. On the lateral edge of the
bone there is a s to u t process which gives articulation to one of four articular processes on the dorsal
ond of th e hyomandibular, the particular process here concerned apparently being the regular anterior
articular h e ad of the hyomandibular, as will be later explained. Immediately dorsal to this articulating
process there is, on th e same edge of th e sphenotic, a sharp process which gives support, on its lateral
surface, to the small postorbital bone; probably also giving insertion to a p a rt of the levator arcus
palatini muscle, though this was not investigated.
Between th e sphenotic and pterotic there is a large and deep dilatator fossa, roofed by the
pterotic and sphenotic, the postfrontal apparently not coming into roofing relations with it. The
anterior wall of th e fossa is perforated by a large foramen which transmits th e ramus oticus.
The PROOTIC is a large bone with orbital and lateral portions, these two portions being
separated from each other by a ta ll and ridge-like edge which, because of the flattened condition