gular surface is broken by the projection of the anterior wall of the tympanic cavity, it slopes backwards
and outwards ; its upper margin extends to the post-temporal process of the mastoid ; the lower is horizontal
and directed to the inferior angle of the paroccipital process.
The roof of the orbit is formed by the frontal, and by the ali-sphenoid, for a short space ànterior to the
temporal fossa ; a line drawn from the optic foramen, through the foramen ovale, to the posterior tympanic
articular facet, will indicate the lower margin of the ali-sphenoid. The inferior boundary of the mastoid corresponds
to a line drawn from the notch between it and the paroccipital process, through the superior tympanic
aperture to the inner angle of the root of the post-temporal process, where it comes into apposition with the
external border of the ali-sphenoid; thence the suture passes forwards, inclining upwards to the post-orbital
process. The division between the sphenoid and the ex-occipital follows the course of the canal which
runs behind the fenestra ovalis ; its upper angle is anterior to the inferior tympanic articular surface,
which is developed on the ex-occipital; below it passes internal to the Eustachian tube, cutting through the
elliptic fossa, common to the foramen caroticum and f. lacerum posterius, and lastly bends transversely
inwards, intersecting the foot of the basilar protuberance. The diminished area of the interorbital septum,
which is only about six lines in diameter, is remarkable, and is due to the small size of the eyes, which are
amply protected by the great outward projection of the roof of the orbit posteriorly. The proper septum is
reduced to the small space, intervening between the base of the olfactory fossæ and the interval separating
the foramina optica, in the antero-posterior diameter ; it is encroached on above by the expanded frontals,
and below by the inflated rostrum. From the abbreviation of the cranium, and consequent shortening
of the frontal, the orbital vault is relatively very small ; it is bent down abruptly anteriorly, nearly at right
angles, and, as it were, pressed backwards ; the angle of flexure corresponding to the supra-orbital notch
from which the roof increases in breadth as it retrogrades obliquely downwards.
A line drawn from the supra-orbital to the temporal notch would ciit off an elongated triangular
segment; thé hypothenuse corresponding to the convex, thick, and rough supra-orbital margin, and the
base to the post-orbital process. The great breadth of the interorbital region, which is continued backwards
diminishing very gradually to the mastoid notch, and the flattening down, as it were, of the roof of
the orbit behind the eye ; together with the great elevation of the forehead above the- surface of the mandible,
and its contraction in front of the supra-orbital notch, are remarkable peculiarities in the head of
this extinct form. The roof of the orbit is arched transversely, but more flatly concave longitudinally than
the anterior portion of the orbital vault ; the greatly increased expansion of the diploë of the frontal internally,
causes its surface to descend rapidly into that of the interorbital septum; while from the retrogression
of the olfactory fossæ, the anterior wall slopes very gradually backwards. A line drawn from the inferior
extremity of the prefrontal to the post-orbital process, measuring one inch and seven lines, ascends
obliquely backwards at an angle of 45°; and a plane extended inwards from it to the optic foramen would
limit the orbit posteriorly and inferiorly. The depijh of the vault from the supra-orbital notch, is one inch
one line.
Th§ foramen opticvm, situated at the apex of the triangularly pyramidal orbital fossa, is equidistant
from the anterior and posterior surfaces of the cranium, and from the supra-orbital and mastoid notches ;
its circular contour is notched above by a vascular groove, and its relatively small diameter is two lines and a
half. Its floor is four lines and a half from the basilar surface, and its roof one inch ten lines and a half
beneath the highest point of the frontal protuberance. The anterior edges of the foramina of opposite sides,
are separated by an interval of six lines and two-thirds, corresponding to the broad posterior border of the
interorbital septum, which is convex transversely, and concave vertically.
The mt-orUtalfwomen, for the transmission of the ophthalmic branch of the trigeminal nerve and
accompanying vessels, is eight lines distant from the foramen opticum, in a direction forwards and upwards,
and midway between it and the ant-orbital process. Its form is irregularly transversely ovate; a ventricose
projection on the left side, encroaches on its area inferiorly. The posterior expanded border of the inferior
ethmoidal aia, is three lines and a half broad. The prefronto-ethmoidal fissure is obliterated; a narrow,
tripartite chink, slightly wider in the centre, alone remaining; the inner branch of which probably corresponds
to the notch between the turbinated and inferior alee, the evasation of the latter to form the large
olfactory fossa being the cause of the disappearance of this fissure, which in other birds transmits the
superior diverticulum of the subocular sinus; the upper indicates the union of the prefrontal to the turbinated
ala; from its extremity an interrupted groove, more distinct on the right side, is directed downwards
and outwards at an acute angle, to the upper margin of the lacrymal groove, defining the antorbital process
as it runs along the outer margin of the body of the prefrontal.
The tumid prefrontal coalesces below with the inferior ala, and is three lines and two-thirds wide; its
broad outer convex surface, beneath the antorbital process, presents the lacrymal groove, more depressed at
its lower margin; it runs forward, inclining inwards, to the outer margin of the olfactory fossa, and is
eight lines in length, and three and a half broad; in the inner part of its course, it rests on a quadrate
process of the prefrontal, which projects beyond the level of the anterior margin, and comes into contact
with the convexity of the turbinated ala; this projection is separated by a notch, from the prominent inner
angle of the body of the prefrontal above, and below from its inferior extremity; which is slightly flattened
and roughened opposite the zygoma, with which it would probably come into contact, in the great downward
flexion of the upper mandible. The ant-orbital process is thick and rough externally, and contracts in its
anterior moiety, into a narrow style, whose apex is at the upper border of the lacrymal groove. Prom the
supra-orbital notch a deep capillary fissure, with small lateral offsets, passes backwards and inwards, on the roof
of the orbit for six lines; it probably lodged a small branch derived from a cutaneous artery. The superciliary
margin1 is perforated about six lines in front of the post-orbital process, by two small foramina on the left
side, but is notched on the right for the transmission of the supra-orbital arteries and veins to the scalp;
internally they correspond to a groove running half an inch in front of, and parallel to, the posterior border
of the orbit; it winds round a tumid projection of the diploe of the ala-sphenoid a little above the foramen
opticum, which it enters, grooving its roof, and disappearing as it curves backwards. A second groove, for
the nasal vessels, runs backwards and upwards from the ant-orbital foramen, to join the supra-orbital furrow
above the prominence just mentioned. Numerous small apertures are seen along the course of these
channels; a faint vascular groove runs from the prefronto-ethmoidal fissure to the centre of the nasal
one; between the latter and the foramen opticum, and bounded laterally by the peculiar pneumatic bullae, is a
quadrate space, variously marked by vascular impressions.
The temporal fossa descends obliquely forwards, sloping inwards, and terminates inferiorly at a deep
digital cavity, impressing the ali-sphenoid behind the optic foramen. It. opens superiorly by the small narrow
oblong temporal notch, five lines in depth, and three and a half in breadth; bounded in front by the short,
thick, post-orbital process, slightly r,ecurved at the apex, and behind by the post-temporal plate of the mastoid.
The small crotophyte impression occupies the temporal gorge, and extends outwards, as the latter is
broadly rounded off into the upper facet, in the form of a crescent, whose limbs extend on the triangular
surface of the post-orbital process, and on the quadrantal post-temporal plate, which is traversed by a slight
chord-like ridge. The internal temporal impression has the figure of a right-angled triangle; below, a
narrow smooth tract separates its base from the surface for the M. Levator ossis quad/rati; the undulated
hypothenuse ascends forwards to the root of the post-orbital process, its upper third being separated by a faint
ridge from the external impression; its surface subsides, anteriorly, about a line beneath the smooth and