MYODOME.
The myodome (eye-muscle canal) of Scorpaena has the shape of a funnel, the body of which
is triangular or semicircular in transverse section, while the tubular portion is nearly circular in section.
The orbital opening of th e canal is approximately an equilateral triangle with rounded corners, the
base of th e triangle being presented dorsally and th e triangle being bisected by the pedicle of the
basisphenoid. The opening is bounded ventrally by the body of th e parasphenoid, laterally on either
side by the ascending process of the parasphenoid, and dorsally mainly by the body of the basisphenoid
though pa rtly also by th e prepituitary portions of the mesial processes of the prootics. At
th e extreme dorso-lateral corner of the opening, is the internal jugular notch, th a t notch lying, as
already explained, between the basisphenoid and parasphenoid legs of th e alisphenoid. From this
notch th e internal jugular groove leads postero-laterally into the trigeminus opening of the trigemino-
facialis chamber, the notch, groove and chamber all being remnants of th e upper lateral chamber of
th e myodome of Amia.
Immediately internal to its orbital opening the myodome expands abruptly a t its dorso-lateral
corners, a pocket thus here being formed, on either side, which, as already stated, projects upward
and reaches the under surface of the th in floor of the trigemino-facialis chamber. The myodome here
has its largest transverse section, and from here contracts rapidly to the hind edges of the prootics,
where the long and relatively small tube of th e funnel begins. This tube lies wholly in th e grooved
ventral surface of th e basioccipital, the body of th e funnel lying wholly between th e prootics. Between
th e ventral edges of these la tte r bones, and also between the ventral edges of the groove in the basioccipital,
there is a long slit-like opening, the hypophysial fenestra. This fenestra extends the full
length of the floor of the myodome b u t is closed, ventrally, by the parasphenoid, excepting a t its
extreme hind end where the myodome opens onto the ventral surface of th e skull. The roof of the
body of the myodome is formed in p a rt by the basisphenoid, b u t mainly by the mesial processes
of the prootics, and it is perforated, in its anterior portion, by the median, p itu ita ry opening of the
brain case.
The pitu ita ry opening is closed, in the recent state, by membrane, and, arising from this
membrane and extending forward to the hind edge of the pedicle of th e basisphenoid, there is a v e rtical
band of tough fibrous tissue, attached by its dorsal edge to the ventral surface of the body of
the basisphenoid. The anterior end of this tissue gives origin, on either side, to the rectus inferior
muscle. The ventral edge of the band spreads, and is firmly attached to the dorsal edges of th e recti
intemi muscles, those two muscles entering the myodome, on either side, ventral to the rectus in ferior,
along the floor of the myodome and close against the pedicle of the basisphenoid. The a tta ch ment
of these recti interni to the ventral edge of the mid-vertical membrane seems to be th e imp
o rtan t origin of th e muscles, for although they extend posteriorly considerably beyond th e membrane,
approximately to th e hind ends of th e prootics, they are, in this p a rt of their course, simply
attached to each other and to loose tissues in th e myodome; the atta chm en t of th e muscles to each
other being strong. The rectus superior, on either side, enters th e myodome near the dorsal end of
its orbital opening, there passing downward between th e rectus inferior, mesially, and th e rectus
externus laterally. Running downward and b u t slightly backward it passes lateral to the rectus
internus and has its origin on the dorsal surface of the parasphenoid. The rectus externus enters
the myodome along the lateral edge of its orbital opening, lying lateral to all the other muscles.
Turning backward in the myodome it lies a t first dorso-lateral to the rectus internus, b u t it extends
posteriorly beyond th a t muscle, into th e basioccipital p a rt of the myodome. Near the hind end of
this la tte r p a rt of the myodome, the muscle becomes tendinous and is inserted on the basioccipital,
certain of the fibers of the tendon passing out of the myodome, by its posterior opening, and there
arising from the ventral, external surface of the bone. The orbital opening of the myodome is closed
b y a strong membrane which th e recti muscles all perforate to reach their points of origin.
Sagemehl says th a t, in the Characinidae, the recti inferior and externus arise in the myodome,
the internus having its origin in the orbit; and as the myodome, in the Cyprinidae, is said to differ
in no important respect from th a t in th e Characinidae, these muscles must there have the same
origin. In all of the mail-cheeked fishes th a t I have examined, and also in Scomber (Allis, ’03), it
is the externus and internus instead of the externus and inferior th a t have this origin in the myodome.
C A R O T I D A R T E R I E S A N D V E S S E L X.
The external and internal carotid arteries were traced both in 45 mm specimens and in the
adult, and they differ b u t little from the arteries in the adult Ophiodon elongatus, recently described
by Allen (’05). I, however, find, in young specimens of Scorpaena, Trigla, Lepidotrigla and Dacty-
lopterus, a small arte ry th a t is not described by Allen, th a t would seem to be in p a rt the homologue
of th e hyo-opercularis artery of my descriptions of Amia (’97, p. 497), and th a t has already been
referred to as the vessel x.
The external carotid of Scorpaena, after its origin from the short common carotid, runs upward
and forward, enters the trigemino-facialis chamber through its facialis opening, and traversing th a t
chamber issues by its trigeminus opening. I t then immediately gives off what must be the sclerotic-
iris artery of Allen’s descriptions, though the artery as I find it has not exactly the distribution given
by Allen. I t then gives off a branch to the levator arcus palatini muscle and the large facialis-maxil-
laris artery, as described by Allen in Ophiodon, and itself turns downward and slightly backward
in th e V-shaped space between two flanges on the hind edge of the metapterygoid, to be later described.
A t the lower edge of the internal one of these two flanges the artery falls into the arteria
hyoidea a t a sharp bend in th a t artery, th a t p a rt of the carotid th a t lies between th e point where
it gives off the facialis-maxillaris and the point where it falls into the arteria hyoidea, corresponding
closely in position to th e secondary afferent pseudobranchial artery of my descriptions of Amia
(’00 c). The hind end of the la tte r artery, in larvae of Amia, closely approaches the dorsal end of the
primary affferent pseudobranchial artery, which artery is the arteria hyoidea, and if the secondary
afferent arte ry should acquire a connection with the arteria hyoidea, and th a t artery retain its connection
with the pseudobranch, the conditions found in Scorpaena would arise. And this is quite
certainly th e manner in which the teleostean arrangement has actually arisen.
The arteria hyoidea of Scorpaena, coming upward along the ceratohyal, turns dorso-anteriorly
along the anterior aspect of the interhyal and traverses a large opening th a t lies between th e pre-
opercular and the posterior process of the quadrate, posteriorly, and the symplectic anteriorly.
There it immediately gives off the mandibular artery, which runs downward and forward, along
the outer surface of the quadrate, into the mandible. Having given off this artery, the arteria hyoidea
turns sharply upward, crosses the external surface of the hvomandibulo-symplectic interspace of
cartilage and a t th e antero-dorsal corner of th a t cartilage passes inward through a small opening
between the cartilage, the metapterygoid and the shank of the hyomandibular. Continuing its upward