on th e outer surface of the exoccipital marks the position of the dorso-lateral portion of this labyrinth
space, and forms a continuation of the ridge on the pterotic th a t marks the course of th e external
semicircular canal in th a t bone.
The dorsal edge of the exoccipital reaches th e ventral surface of th e overhanging roof of the
skull and is there separated by a relatively wide band of cartilage from th e ventral edge of the
pterotic, th a t edge of th e la tte r bone here being presented mesially. This band of cartilage forms a
nearly longitudinal line along the bottom (roof) of th e subtemporal fossa, and lies against the ventral
surfaces of th e parietal and lateral extrascapular.
On the hind edge of the lateral plate of th e exoccipital there are two flat s to u t processes separa
ted by a deep and rounded incisure. The dorso-lateral process suturâtes with th e pedicle of the
suprascapular, the ventro-mesial one suturating with, instead of articulating with, a process on the
anterior edge of th e first vertebra. Antero-internal to th e incisure between th e bases of th e two
processes, a canal traverses the medullary p late of th e bone, transmitting the occipital nerve o r nerves.
Ventrally th e exoccipital suturâtes with the basioccipital, in th e manner already explained. On
th e lateral surface of the bone there is a small foramen which doubtless transmits th e nervus
glossopharyngeus, and posterior to th a t foramen there is a large pit, in th e bottom of which there
are two to four foramina which open into the cranial cavity and doubtless transmit the nervus
vagus alone; the actual relations of these nerves to th e bone not being determined for th e reasons
already given.
The EPIOTIC is a small bone th a t seems a t first sight to bear no resemblance whatever to
the pyramidal bone of th e other fishes of th e group. The dorsal surface of the bone is flat and sub-oval
in shape, and on th e ventral surface of this th in dorsal plate there are two relatively ta ll and thin
flanges. One of these flanges is straight and extends from about the middle of th e mesial edge of
bone, postero-laterally to its lateral edge, the ventral edge of the flange suturating with th e posterior
plate of th e exoccipital. The postero-mesial surface of this flange is exposed externally, and forms
a surface strictly comparable to th e postero-mesial surface of the bone in th e other fishes of the group.
The second flange lies anterior to the first one and is strongly curved, the hollow of the curve directed
forward and both ends of th e flange reaching the antero-lateral edge of th e bone and there vanishing.
The space enclosed within the curve of this flange is roughened and suturâtes with th e dorso-mesial
surface of th e lateral plate of the exoccipital, as already stated. This roughened surface of the
epiotic thus corresponds to the ventral edge of th a t surface of the bone in the other fishes th a t forms
p a rt of the mesial wall of th e temporal groove. The temporal-groove surface of the bone of Dactylo-
pterus is accordingly wholly wanting, or a t most is only represented in a p a rt of the th in lateral edge
of the bone, this edge being covered laterally and ventrally by the band of cartilage already described
between th e pterotic and exoccipital.
Between th e two flanges on th e ventral surface of the epiotic there is a space which forms
th e dorsal portion of th a t p a rt of th e labyrinth recess which, as ju s t above explained, must lodge
th e posterior semicircular canal and th e posterior portion of th e external canal. The dorso-postero-
lateral portion of this labyrinth space is bounded externally here ventrally by the band of cartilage
between th e p terotic and exoccipital; temporal and posterior surfaces of the epiotic n o t here uniting
to form an angle which encloses th e summit of the posterior canal, as in the other fishes. The large
fla t dorsal surface of th e epiotic gives support to adjoining portions of the parietal, lateral ex tra scapular
and mesial extrascapular, and its mesial edge is in sutural contact with the lateral edge
of the supraoccipital. The th in plate th a t forms this p a rt of the bone projects posteriorly beyond
th e flange th a t forms th e posterior surface of the bone, the two plates forming p a rt of the roof and
p a rt of th e bottom (antero-lateral corner) of a large fossa on th e posterior surface of th e skull. The
postero-lateral end of the flange th a t forms the posterior surface of th e bone, and adjoining portions
of the lateral edge of th e bone, suturate respectively with the pedicle and body of the suprascapular.
The SUPRAOCCIPITAL, the interparietal of Cuvier and Valenciennes’ descriptions, has
the usual dorsal and ventral limbs, and a large spina occipitalis. The dorsal limb of the bone, with
the exception of two small lateral processes on either side, comes everywhere to th e outer level of
th e dorsal surface of the skull, and has surface markings exactly similar to those on the adjoining
dermal bones; and this apparently dermal portion of this limb of the bone extends posteriorly
slightly beyond the line of origin of the v entral limb, onto th e dorsal surface of a dorsal plate-like
portion of th e spina occipitalis. This limb of the bone suturates anteriorly with the frontals, laterally
with the parietals, and posteriorly with th e mesial extrascapulars; its anterior edge resting, on
either side, upon the hind end of the expanded dorsal surface of the brace-like ridge on the internal
surface of the alisphenoid. On the ventral surface of the dorsal limb, beginning immediately anterior
to the line of origin of the v entral limb, there is, on either side, a small ridge which, extending antero-
laterally is continuous with th a t tall ridge on the internal surface of th e prootic th a t forms the anterior
wall of th e labyrinth recess. The antero-lateral end of this ridge on the supraoccipital forms one of
the two lateral processes on either side of the dorsal limb of the bone, the other process lying
immediately posterior and parallel to it, giving support on its dorsal surface to th e parietal, and being
in synchondrosis, by its postero-lateral edge, with the antero-mesial edge of th e epiotic.
The ventral limb of the supraoccipital is irregular, as shown in the figures, and has on either
side a strongly concave dorsal and convex ventral surface. Along the median line of the limb a thin
median vertical plate of bone arises supported on either side b y a similar b u t slightly inclined plate,
these three plates forming the vertical portion of the spina occipitalis. This vertical portion of the
spina supports, on its dorsal edge, a flat broad th in plate which forms a direct posterior extension
of th e dorsal limb of the bone, and gives support, on either side of its dorsal surface, to th e corresponding
mesial extrascapular. The lateral edge of the anterior end of this flat portion of the spina,
on either side, rests upon and is coalesced with the dorsal edge of the lateral portion of th e ventral
limb of the bone, a deep pocket thus being formed on either side of the posterior surface of the bone,
this pocket forming the dorso-mesial corner of a large fossa on either side of th e hind end of th e skull.
The posterior half of th e ventral surface of th e ventral limb of the bone rests, on either side, on the
dorsal edge of the medullary plate of the corresponding exoccipital, either-suturating or being in
synchondrosis with th a t bone. Lateral to the exoccipital, th e ventral limb of the supraoccipital
is in similar contact with the mesial edge of the epiotic.
There is no separate OPISTHOTIC bone, nor is there any indication of the fusion of this bone
with any of th e other bones.
The p rimary bones, and their relations to the dorsal surface of the primary skull, now having
been described, th e dermal bones th a t overlie them and form th e casque-like dorsal surface of the
skull can be described.
The two NASALS have fused in the median line to form a single median bone, and have
already been described.