of the two branches are given off and pass along theinner aspect of the extremity
of the orbitofrontal plate to the orbit. Where the optic canal opens into the
s p h e n o i d a l canal the optic nerve is superior to the divisions of the fifth, which it
crosses to reach the orbit; In passing a bristle through the canal it is frequently
stopped in its progress by abutting against the outer wall of the sphenoidal canal
opposite its own exit from the orhitosphettoid, and it is this which sometimes
makes the bristle return, into the skull by the sphenoidal fissure. In young, and
even in some adult, skulls the optic canal shows an imperfection of ossification
immediately above the pterygomasillary fissure, its walls being thin and almost
transpare ^ ^ narrow elongated surface on which the external basal
borders of the maxillary crests rest. I t is directed downwards and f orwards. narrow-
ing towards its upper extremity, which is placed over the median lrne of the temporal
fossa. The middle of its posterior border is marked hy a deep notch, which
h e s t d e f i n e d o n t h e r i g h t s i d e i n a d u l t s k u l l s . . .
The zygomatic process of the temporal (z, fig. 2, El. XXXIX) is received
into a pit on the hinder margin of the lower end of the facial portion, immediately
behind or above the level of the superior border of the orbit, so that
there is no postorbitel process. In adult skulls, the inner surface of the anterior
end of the zygoma is sheathed by a thin plate of bone from the front wall of
the temporal fossa. Anterior to the zygomatic pit is the crescentic upper margm
of the orbit, which is a more or less triangular cavity, the apex of which is directed
inwards and backwards. I t has a depth of about 1-50 inch m adult skufis, wrthan
anterior diameter of not more than one inch, The inner wall is chiefiy formed by
the thickened base of the malar, its roof being essentially frontal. Its floor is very
narrow and is formed exclusively by the backwardly and outwardly projecting
zveomatic process of the malar, which abuts against the zygomatic process of the
squamosal; in this respect the orbit of this dolphin is more normal, so to speak,
than the orbit of such forms as Gloticephalm, Orcella and their allies. The
malar vertical diameter of the orbit is little over half an inch The m a t a floor
does not project so far forwards as the upper frontal border of the orbit, but the
deficiency is made up in life by a strong fibrous tissue which invests the eyeball and
is external to the malar and to the frontal margin, so that the minute globe is almost
external to its orbit. „__MR
The temporal, which is continuous with the orbitotemporal plate of the frontal,
but directed downwards, backwards and outwards, is triangular and received between
the parietal and pterygoids. „ „ a , Q, rm.„.
Squamosal (PI. XXXIX, figs. I and 2, and El, XL, figs. 8 and 9). The
distinguishing features of this bone are the great size and strength of its zygomati
arch, the remarkable postglenoid fossa and the strong downward^ tad mwarcfly
projecting process which embraces the petrous and is apphed to the.outersurface
of íheupperposterior extremity of the pterygoid and abuts against the anterior
border of the tympanic.
The squamous portion is nearly vertical, and the lower border of its rough
inner surface projects downwards and inwards; its base or under surface below this
border being deeply concave and maiked with numerous foramina and forming a
cavity into which the outer wall of the petrous bone is received. The hinder
border of the squamous portion is marked by a fine ridge passing downwards,
outwards and forwards to the posterior margin of the base of the zygoma.
Behind this ridge, and projecting downwards and backwards from the squamous
portion and forming one-half of the upper boundary in young skulls, and in adults
the whole of the posterior wall of the external auditory meatus, is a nipple-shaped
postauditory process simulating a mastoid. To the inside of this process the
periotic and tympanic are firmly attached, and do not project behind its external
margin, although the posterior border of the rough surface of the tympanic, which
is attached to this process and the posterior fang of the periotic abut against the
anterior border of the exoccipital; yet the fixedness of these two bones depends
entirely on the attachment to this process. Internally this plate presents a nearly
vertical pit into which the anterior fork of the mastoid is received and wholly
invested. The outer surface of the posterior wall of this pit has the second fang-like
process of the periotic applied to it. To the outside of the inner wall of the pit, the
rough surface ( vaginal) of the tympanic is applied; also investing the posterior
fang of the mastoid and the styloid process. The posterior border of this process
articulates with the exoccipital, to which it only becomes united in very old skulls.
The lower border of the parietal surface of the squamosal, which is at a considerably
higher level than the pit, projects inwards as a thin plate with the upper internal
border of the pit, constituting a broad longitudinal furrow, in which lies the anterior
division of the periotic.
The zygomatic process of this skull, as is well known, is remarkably large
and has a considerable outward curve. I t is very deep at its base, but its anterior
extremity is narrowed to one-half of the vertical height of the former part and
is applied to the frontal forming the posterior border of the orbit. The superior
border is nearly longitudinal, with only a very slight upward tendency, while
the lower convex border has a decided upward and forward curve. The external
surface is markedly convex and the internal, deeply concave; so much so, that
the powerful-looking bone has no commensurate thickness and is occasionally
fractured. At its base above there is a groove for the temporal muscle. The posterior
basal margin is concave, and at its. upper end, in adults, it forms an arch over
the' external auditory meatus, springing from the anterior surface of the post-
auditory process; while, in young skulls, this process forms the whole of the upper
external boundary of • that opening. Its lower end is directed backwards and
inwards, terminating in a rough postglenoid border, from which a thin, inwardly projecting
plate is prolonged upwards and forwards in a curved manner to the anterior
root of the petro-pterygo-tympanic plate. This glenoid plate c6nstitutes part of the
floor and of the external wall of the deep fossa that occurs on the inner surface of
the base of the zygoma. On the inner wall of this fossa, between the periotic and
r 3