of the head, lies in a nearly horizontal position directed postero-laterally and b u t slightly upward.
This ridge-like postorbital edge is perforated by a large opening which represents the trigemino-
facialis chamber, and from this chamber five foramina lead into th e cranial cavity. One of these
foramina transmits the truncus ciliaris profundi accompanied by th e encephalic branch of th e jugular
vein; a second one transmits the ramus ophthalmicus lateralis; a third the truncus trigeminus and
related lateralis nerves, and a fourth th e truncus facialis. The fifth foramen certainly transmits
the nervus abducens, and probably th a t nerve alone, th e palatinus facialis doubtless traversing the
facialis foramen, b u t these nerves were n o t traced in th e adult. In 5 cm specimens, they both traverse
th e ventral portion of th e facialis foramen, enter the trigemino-facialis chamber, and traversing
th a t chamber, issue through its trigeminus opening. The chamber is also traversed, as usual, by
the jugular vein and th e truncus sympatheticus.
Dorsal to the trigemino-facialis chamber, the tall postorbital edge of the prootic expands
abruptly and bears, on this expanded portion, an elongated and curved articular surface the axis
of which is directed dorso-posteriorly while the surface itself is directed laterally. This surface gives
sliding articulation to a curved surface on the anterior one of the four articular heads of the hyoman-
dibular. Slightly dorsal (here lateral) to this articular surface the bone is connected by synchondrosis
with the sphenotic.
The orbital portion of th e prootic is large, is transverse and nearly vertical in position, inclining
upward and slightly forward, and arises from th e internal surface of th e lateral portion of th e bone
slightly posterior to its anterior edge. Near its dorsal edge it is perforated by th e oculomotorius
foramen. I ts mesial edge does not reach th e m iddle line, a small v entral portion of th e edge suturating
with the transverse ridge on th e dorsal surface of th e parasphenoid, while th e dorsal portion of the
edge is free and forms p a rt of th e boundary of th e p itu ita ry opening. The lateral portion of th e bone
has its ventro-mesial edge bevelled on its outer surface, and there suturates with th e lateral edge
of th e parasphenoid. Internal to this line of sutural contact, and posterior to th e orbital portion of
th e bone, th e edge of th e prootic is slightly grooved and this groove lodges th e lateral edge of a broad
band of cartilage which extends across th e middle line to th e corresponding edge of th e prootic of th e
opposite side. The h ind edge of th e band is lodged in a groove on th e anterior edge of th e basioccipital,
its anterior edge reaching to th e posterior surface of th e transverse ridge on th e dorsal surface of the
parasphenoid. This anterior edge of th e cartilage seems not to be a free edge, b u t to ra th e r abruptly
b u t insensibly pass into a delicate membrane which is connected, anteriorly, with th e stouter membrane
th a t fills th e pitu ita ry opening of th e brain case. Two suppositions are accordingly possible
to explain th e conditions here; either th e p ostpituitary portion of th e prootic bridge has been depressed
and appressed upon the underlying ventral flanges of th e prootics, as assumed b y Gill (’91a, p. 379)
in his descriptions of Hemitripterus, or th e entire prootic bridge has been shortened and shoved
forward nearly to th e anterior edges of th e ventral flanges of th e prootics and there tilted upward
to form, on either side, th e orbital portion of th e corresponding bone. The conditions found in
Blennius, to be la te r described, indicate th a t th e first of these two assumptions is probably th e p roper
one, b u t th ey also indicate th a t the process has n o t been simply one of depression and appression
of th e prootic bridge, b u t also one of reduction of th e ventral flanges of the prootics. These ventral
flanges have, apparently, been so greatly reduced th a t they are practically suppressed, and the
primary floor of th e cranial cavity is here formed by th e prootic bridge alone, th a t bridge lying
directly upon the parasphenoid. The hypophysial fenestra is then represented, in its posterior
portion in th a t long and wide space th a t lies between those surfaces of the prootics of either side
th a t suturate with th e lateral edges of the parasphenoid, while in its anterior portion it is
represented in th e space th a t lies between and anterior to th e orbital portions of the prootics,
th is space opening onto the floor of th e myodome and being filled by the transverse ridge on the
dorsal surface of the parasphenoid. This la tte r ridge on th e parasphenoid is accordingly the greatly
shortened and widened homologue of the longitudinal ridge on th e bone in the other fishes of the
group. A result of this arrangement is th a t th e p itu ita ry opening of th e brain case is partly filled,
toward the orbit, by th e transverse ridge on th e parasphenoid, and th a t th e hind end of the pituitary
opening is confluent with th e hypophysial fenestra a t the hind end of th a t portion of the fenestra
th a t opens onto the floor of th e myodome.
The lateral surface of the prootic has dorsal and ventral regions separated by a pronounced
b u t rounded angle which s ta rts from th e dorsal edge of the trigemino-facialis chamber and runs
postero-mesially to the hind edge of the bone. The dorsal portion of th e surface forms the anterior
portion of a large subtemporal fossa, described below. On the internal surface of the bone, and
parallel with this dorsal portion of its lateral surface, there is a tall flange of bone which projects
from below upward and forms the anterior wall of the labyrinth recess. The dorsal edge of this flange
is p a rtly capped with cartilage and there gives support to th e hind edge of th e frontal and to the
parietal, th e hind edge of the flange projecting postero-mesially beneath the supraoccipital and there
being continuous with a slight ridge on th e internal surface of th a t bone. The deep ta ll space between
the flange and th e lateral wall of th e bone is continued dorso-antero-laterally by a slight recess on the
internal surface of th e sphenotic, and th e large recess thus formed between the two bones lodges
n o t only the anterior semicircular canal and th e anterior portion of th e utriculus, b u t probably also
th e anterior end of the sacculus, for there is no differentiated saccular groove. The recess must
also lodge an anterior portion of the external semicircular canal, for th a t canal leaves the recess
near its dorso-antero-lateral corner to enter it own special canal in the pterotic. The exact relations
could not be determined because of the want of sufficient material.
Anteriorly th e prootic is bounded by, and is pa rtly in synchondrosis and pa rtly in sutural
connection with th e alisphenoid. Dorsally and posteriorly it is in similar relations with the sphenotic,
pterotic, basioccipital and exoccipital. Ventrally it is overlapped externally by and is suturally
connected with th e parasphenoid.
The PTEROTIC has, more th a n in the other fishes of the group, the appearance of being
formed of two separate and independent components secondarily fused with each other, for, although
th e two components have th e same length, they are not exactly superimposed; the dermal component
projecting forward beyond the primary component, and this la tte r component projecting posteriorly
beyond th e dermal one. This projecting portion of the primary component supports the anterior
edge of th e suprascapular.
The dermal component of the bone is bounded, as usual, by th e frontal, postfrontal, parietal,
lateral extrascapular (rocher) and suprascapular, and the lateral half of this p a rt of the bone is bent
a bruptly downward, as are also corresponding portions of the postfrontal and suprascapular, a rounded
longitudinal angle thus being formed, which extends across the three bones and terminates, a t teh
hind end of the suprascapular, in a strong spine. This component of the pterotic is thus an angular
bone placed longitudinally along th e lateral edge of th e dorsal surface of the skull. I t is traversed
by the main infraorbital latero-sensory canal and lodges three sense organs of th a t line, two innervated