T E M P O R A L F O S S A .
The temporal fossa of fishes is a hole formed by th e more or less complete roofing, by dermal
bones, of th e temporal groove on the dorsal surface of the primordial cranium. This fossa and groove
are both shown in w hat is considered as th e most primitive condition known, in Amia calva, in which
fish they have b o th been described by Sagemehl (’83); b u t Sagemehl did n o t recognize, in this fish,
an anterior extension, or diverticulum of th e groove, to which I later called attention (’89, p. 501),
and which becomes incorporated in th e groove and fossa in certain other fishes, as shown below.
In Scorpaena scrofa the temporal groove is deep, b u t short, antero-posteriorly, as compared
with th a t of Scomber, corresponding only to th e deeper, posterior portion of my descriptions of th e
groove in the la tte r fish. The groove is, in Scorpaena, completely roofed, mainly by th e lateral extra-
scapular and suprascapular bones; b u t there are, along th e edges of th e groove,overhanging portions of
th e p terotic, epiotic and p arieto-extrascapular, and between th e edges of th e parieto-extrascapular and
lateral extrascapular, there are narrow spaces spanned by tough fibrous tissue. The groove being
completely roofed, becomes a fossa, and opens onto the posterior surface of th e skull by a large opening
which occupies th e dorso-lateral portion of th a t surface. A small opening between th e hind edge of
th e pterotic and the opisthotic process of th e suprascapular, leads into the fossa from th e lateral
surface of the skull, and through this opening th e supratemporal branch of the n ervus lineae lateralis,
accompanied by certain vagus fibres, passes inward into th e fossa. The mesial wall of the fossa is
formed by th e epiotic; its lateral wall by th e pterotic, the opisthotic, and the opisthotic process of
th e suprascapular. Its floor is formed in p a rt by th e sloping side walls of th e pterotic an d epiotic,
b u t mainly by a relatively wide strip of cartilage which separates those two bones, and which is the
temporal interspace of my descriptions of Scomber. Posteriorly th is interspace of cartilage is bounded
b y the dorsal edge of th e exoccipital, which bone forms th e floor of th e posterior opening of th e fossa,
and, in large specimens, a small p a rt also of th e floor of th e fossa itself.
The fossa lodges, as in other fishes, an anterior extension of the tru n k muscles, and if those
muscles were to push forward and upward, through th e space covered by th e lateral extrascapular,
onto th e dorsal surface of th e sk u ll, they would push forward dorsal to th e parietal portion of the
parieto-extrascapular and dorsal also to th e depressed hind edge of the frontal, and, occupying th e
region between th e mesial and lateral rows of spines, would give rise to th e temporal groove of Scomber.
In one specimen, in which th e parieto-extrascapular had been removed from th e underlying
bones, th e dorso-anterior end of th e temporal groove formed a sort of pocket which is apparently
th e homologue of th e recess in th e antero-lateral corner of th e groove in Scomber (’Allis, ’03, p. 51),
and th e homologue also of th e anterior diverticulum of the groove in Amia. The pocket, in Scorpaena
, opened onto th e dorsal surface of the primordial cranium by a small and separate opening,
which lay immediately anterior to th e suturating edges of the superficial portions of th e epiotic and
auto-pterotic, between those bones and a portion of th e chondrocranium, and was covered externally
by th e parieto-extrascapular.
In th e Elopidae and Albulidae, th e former of which are said b y Ridewood (’04a) to be th e most
archaic of existing teleosts, and the la tte r to be in b u t few respects more highly specialized, th e temporal
fossa is said to be very extensive. Ridewood calls this fossa th e posterior temporal fossa, and
says th a t it extends forward a considerable distance beneath th e frontal; apparently extending even
a certain distance between th e orbits, for in addition to the prootic, sphenotic (postfrontal, Ridewood)
and supraoccipital, Ridewood says th a t th e alisphenoid, and even the orbito-sphenoid form, in one
or other of th e fishes described, a p a rt of its floor.
Dr. E. C. Starks, of Stanford University, having most kindly sent me two specimens of Elops
and a few specimens of Albula, I have examined th e temporal fossa in both of these fishes. In Elops,
I find th a t th e posterior portion only of th e fossa is th e homologue of the entire fossa of Scorpaena.
This posterior portion of th e fossa is much shorter and much less important th an the anterior portion,
and is separated from th e la tte r portion by a wide and evenly rounded transverse elevation of the
floor of th e fossa. This transverse elevation, or saddle, separates th e fossa into two portions, which
have th e appearance of having been primarily more or less independent, and only secondarily united
to form a single continuous groove. The anterior portion apparently corresponds to th e anterior
diverticulum of th e temporal groove of Amia, th e posterior portion corresponding to the temporal
groove itself of th a t fish.
The lateral wall of th e posterior portion of the fossa is formed by the pterotic and opisthotic,
its mesial wall by the epiotic and supraoccipital, and its floor by the pterotic, th e exoccipital, and the
temporal interspace of cartilage. In th e mesial wall of this posterior p a rt of the fossa there is a deep
depression which is certainly the homologue of th e preepiotic fossa of Ridewood’s descriptions of
Clupea, though th a t author does not, in Elops, so define it.
The saddle between the anterior and posterior portions of the fossa is formed, in Elops, mainly
by th e pterotic, th e saddle arching over th e subtemporal fossa and forming its roof. On th e summit
of the saddle th e layer of bone separating the two fossae is so thiiL th a t a slight further excavating of
the bone, on either side, would b reak down the bony separating wall and either p u t the two fossae into
direct communication, or leave them separated by membrane only. This la tte r condition is said by
Sagemehl (’91, p. 555) to be found in Rasbora and Leptobarbus of the Oyprinidae.
The floor and side walls of the anterior portion of th e fossa are formed by the pterotic, prootic,
sphenotic and alisphenoid, th e p a rt of the alisphenoid here concerned being a p a rt of a well developed
flange on th e internal surface of the bone together with th a t p a rt of the internal surface of the bone
th a t lies postero-lateral to th a t p a rt of the flange. This flange of the alisphenoid is continuous v entrally
with a ridge on the internal surface of the prootic, this ridge forming th e anterior wall of the labyrinth
recess. The anterior semicircular canal, running upward and laterally, lies postero-lateral to the
ventral portion of th e flange, in a recess in the alisphenoid, and, as this recess is bridged by a narrow
b a r of bone, the dorso-anterior end of the semicircular canal lies in a short canal in th e alisphenoid.
The sphenotic comes into no bounding relations to the labyrinth recess, being wholly excluded from
it and also from all bounding relations to the cranial cavity, by th e deep anterior portion of th e tem poral
fossa. If this condition of th e sphenotic is primary, its bounding relations to the anterior semicircular
canal are evidently a secondary acquisition, and th a t the condition is primary would seem
to be indicated by its being found in this primitive teleost, in Amia, and also in Esox. In neither
of these three fishes does th e bone extend through the cranial wall; and it accordingly m ust h ave been
first developed, wholly independent of the anterior semicircular canal, simply to strengthen the post-
orbital process of the skull and to give a proper surface of attachment to the muscles th a t have their
origins there. A similar origin is ascribed by Gaupp (’03) to the autopterotic in Salmo.
In the deepest point of th e anterior portion of the fossa there is, in th e prootic bone, a small
circular opening. From this opening a canal runs a t first downward in the prootic to the dorsal edge
Zoologies. Heft 57. 2