dorsal surface of the lateral edge of th a t bone ends in a spine th a t would seem to be th e exoccipital
of Jo rd an & Evermann’s descriptions. Posterior to this suprascapular spine, and in line with it, th e
dorsal edge of th e supraclavicular ends in a more or less pointed corner, b u t there is here no regular
spine. Between th e pterotic spine and th e anterior end of the suprascapular spinous ridge, the lateral
edge, or the postero-lateral corner, only, of the lateral extrascapular intervenes; and on th a t corner
there is a small sharp prominence, ra the r th a n spine. This prominence forms th e postero-lateral
end of a small ridge which extends, from there, antero-mesially across th e dorsal surface of the bone.
These several additional spines thus form a lateral row on th e dorsal surface of the skull, one
or more of th e spines being found on each of the dermal bones th a t form the lateral portion of the
dorsal surface of th e skull, th e lateral extrascapular excepted. B ut it is to be noted th a t th e post-
frontal spines lie lateral to the anterior end of th e pterotic spinous ridge, and th a t th a t ridge is
continued anteriorly by th e slight ridge, already described, th a t leads toward th e point from which
the frontal commissure arises from th e supraorbital canal.
Between th e hind ends of th e lateral and mesial rows of spines, there is a short row of two
small spines, one on the hind edge of th e lateral extrascapular and th e other on th e hind edge of
th e epiotic process of th e suprascapular.
Considering, now, the posterior portion only of th e dorsal surface of th e skull, there are seen
to be, on each side, four ridges or lines of ridges diverging approximately from th e frontal spine.
One of these ridges is the commissural ridge, which extends postero-mesially to th e mesial edge of
th e frontal; and another is th e postocular spinous ridge which extends almost directly laterally to
th e lateral edge of th e same bone. Between these two ridges are th e parieto-nuchal and pterotic
ridges, both extending backward, b u t diverging. These four ridges thus divide the posterior portion
of th e dorsal surface of th e skull of Scorpaena into three regions which are seen to be strikingly similar
to th e regions occupied by the supratemporal, temporal and dilatator grooves of Scomber (Allis,
’03); and th e three grooves of Scomber would arise if the three regions in Scorpaena were to undergo
a depression, this depression being accompanied b y a diminution in size and a backward translation of the
lateral extrascapular, and by a separation of th e postfrontal from th e underlying bones of th e skull.
S U B Q U A D R A N G U L A R G R O O V E .
The subquadrangular groove on th e vertex of Scorpaena is a single median depression, which
occupies th e position of the two supratemporal grooves, united, of Scomber. Laterally it is bounded,
on either side, in p a rt by the parietal spinous ridge, and in p a rt by th e ridge th a t runs backward
from th e base of the frontal spine immediately lateral to the parietal spinous ridge, this second ridge
bearing no spine. The anterior edge of th e groove is reentrant, and is formed, on either side, by the
corresponding commissural ridge. Posteriorly th e groove is bounded by a transverse ridge on the
dorsal surface of th e supraoccipital, this ridge being heightened by superimposed, transverse sutu-
rating processes of the parieto-extrascapulars. The parietal spine lies a t the lateral end of this tran s verse
ridge, and hence a t th e postero-lateral comer of th e groove. The frontal spine lies a t th e anterolateral
corner of the groove. The floor of the groove is formed mainly by the frontal and parieto-
extrascapular bones, b u t a small median portion of th e supraoccipital is exposed near the middle
point of th e groove. These same three bones, on either side of th e head, form th e floor of the larger,
anterior portion of the supratemporal groove of Scomber, the extreme posterior portion of the floor
of the groove, in this la tte r fish, being formed by th e supraoccipital and epiotic. The groove, in
"Scorpaena, thus seems to represent the fused anterior portions only of the supratemporal grooves
of Scomber. The posterior portions of the grooves of the la tte r fish must accordingly be looked for
•elsewhere in Scorpaena, and they would seem to be represented, in this la tte r fish, in two small
pockets, one on either side, which occupy what is, in appearance, the dorsal portion of the posterior
■surface of th e skull. The pockets lie on a dorsal, shelving portion of th e posterior surface of th e skull,
this shelving portion being separated from the portion ventral to it by a distinct angle, usually produced
into more or less of a ridge. This ridge is transverse and nearly horizontal in position, corresponds
approximately to the hind edge of th e dorsal surface of the skull of Scomber, and appears as
th a t edge of the skull of Scorpaena when the dermal bones are removed (Fig. 7).
There are thus two hind edges to the supratemporal portion of the dorsal surface of the skull
of Scorpaena, an antero-dorsal one formed by the dermal bones, and a postero-ventral one formed
b y the primary bones. The development of these two edges I have not a ttempted to investigate,
b u t th e space between them evidently represents the extent to which the trunk muscles have invaded
th e dorsal surface of th e skull in th e supratemporal region. This supratemporal invasion is distinct
from the one th a t enters th e temporal fossa, and its extent, which varies greatly in different fishes,
'seems to be in some way related to the development of the extrascapular bones and the latero-sensory
•canals they carry. Where th e mesial extrascapular elements are strongly developed, meet in the
middle line, or are fused with the parietals, th e trunk muscles pass dorsal to the hind edges of the
bones and stop when, or before, they reach the commissural canal: while where the bones are feebly
■developed, or not fused with the parietals, the invading muscles seem to push them apart, to pass
forward beneath them and th e canal they carry, and then onward, dorsal to th e more anterior bones.
To th e first mentioned, and probably more primitive category belong Polypterus, Amia, Lepidosteus,
Dactylopterus, and all those teleosts in which the mesial extrascapular elements have fused with the
p arietals (Allis, ’04); while to the second category probably belong the larger number of teleosts,
Scomber being typical of th e class. The line th a t marks, in fishes, the anterior limit of th e surface of
invasion of the tru n k muscles, has been called by Sagemehl (’84b) the linea nuchae, and it forms,
in many fishes of the first above-named category, the apparent, and is usually there considered as
th e actual hind edge of the skull. I t is, however, in reality, th e secondary h ind edge of the skull,
the primary h ind edge underlying it and being formed by the hind edges of the dorsal surfaces of
th e primary bones of the skull. The possible presence of these two edges must always be borne
in mind, for it is of importance in comparisons of the region.
In Scorpaena, the two little pockets, ju s t above described, accordingly lie on what is probably
th e posterior portion of the dorsal surface of th e skull, and not on its posterior surface. The mesial
half of the floor of each pocket is formed by a p a rt of the supraoccipital, the lateral half being formed
in p a rt by the epiotic, and in p a rt by the dorso-posterior surface of a flange of bone th a t projects
downward backward and mesially from the ventral surface of the parieto-extrascapular, not far from
its hind edge. This flange lies on th e dorsal surface of the primary skull, and notwithstanding its
apparent origin from the ventral surface of th e parieto-extrascapular should probably be considered
as a p a rt of the dorsal surface of th a t bone. The apparent hind edge of the parieto-extrascapular,
•of either side, projecting backward, forms the roof of the corresponding pocket, and the two pockets
are separated from each other by the spina occipitalis. A p a rt of the epiotic, together with overlying
parts of the suprascapular and parieto-extrascapular, separate each pocket from th e dorsal portion
•of th e corresponding temporal fossa.