processes, is one inch six hues and a half; and its depth from the upper margin of the foramen magnum,
ten lines and a half; from the mesial line obliquely to the angle of the paroccipital process, is one inch
two lines. The longitudinal diameter of the inferior segment is eleven lines and two-thirds; and the
span of its lateral boundary is eight lines and a half. The span of the anterior margin between the apices
of the basilar protuberances, is eight lines and a half. The basi-occipital is three lines and a half thick.
The inferior facet of the cranium exhibits, on each side, the great orbito-temporal excavation, separated
by the short but broad and tumid sphenoid, which expands to join the basi-occipital posteriorly; it is most
constricted at the junction of its posterior and two anterior tliirds, opposite the foramen opticum; it
increases in breadth, as it advances, to where it is joined by the inferior ethmoidal ala on each side; it then
rapidly becomes narrower, and forms a compressed plate projecting forwards into the inferior nasal fissure.
The inflated lower ala of the ethmoid coalesces externally with the bullose inferior extremity of the
prefrontal; which, from the compression of the cranium anteriorly, is prolonged forwards; a deep narrow
notch, leading into the olfactory fossa, separating it from the rostrum. The greatest width of the sphenoid,
between the outer margins of the tympanic tubes, is one inch, eleven lines and a half; its extreme length
is two inches, six lines and a hah"; where most constricted it is six lines and two thirds broad. The distance
between the outer surfaces of the inferior extremities of the prefrontals amounts to one inch, eight lines
and a half; the thickness of the sphenoid at the foramen opticum is four lines and a half.
The lozenge-shaped concavity on the sphenoid, for the insertion of the fleshy fasciculi of the Recti
capitis antici muscles, is deepened posteriorly and laterally by the anterior surface of the basilar protuberance,
which is directed, on each side, inwards and backwards, sloping outwards as it descends to the
apex; anteriorly and laterally a slight ridge separates it from a venous impression on the side of the
sphenoid. The anterior angle projects in the form of a small, free, triangular plate, curving downwards
beneath the transversely ovate common orifice of the Eustacliian tubes; the posterior corresponds to the
median notch between the inner angles of the basilar protuberances. This surface is distinctly pitted on
each side of an irregular raphe: and its antcro-posterior diameter is eight lines.
A groove, two lines broad, running forwards from the orifice of the Eustachian tubes, impresses the
sphenoid where most constricted, and ceases after a course of four hues with a rounded termination; its
edges are sharp, and separate it from the lateral venous impressions; it is lined by the sinus leading to the
Eustachian tubes.
Anteriorly the sphenoid is raised into an obtuse median ridge, between the flattened oblong surfaces
on which the palatine and pterygoid bones glide, in the movements of the upper mandible.
The inferior aspect is concave upwards, deepest opposite the foramen opticum, declining in front to
the lowest part of the rostrum, and behind to the under surface of the occipital condyle, which is in the
same horizontal plane as the former.
The lateral aspect of the cranium is occupied by the large orbito-temporal fossa, winch presents the
form of an irregular, four-sided pyramidal excavation; the floor and inferior wall of which are removed,
lis different surfaces converge to the optic foramen; the posterior is of less height than the anterior, the
upper descending as it retrogrades.
The anterior subconcave wall, is formed in its anterior moiety by the prefrontal, and by the united
turbinated and inferior a\x of the ethmoid; posteriorly it is constituted by the enormously thick, but contracted,
inlerorbital septum; it slopes gradually inwards and backwards, and above is rounded off info the
roof of the orbit. A line drawn from the post-orbital process to the optic foramen, divides the orbital from
the narrow, depressed temporal fossa, which inclines forwards, as it descends inwards. The posterior trian-
Y
magnum has an ovate form, subangular above; it is six lines and a half high, and nearly live lines broad,
inferiorly; the vestibular elevation in the interior of the cranium, projects on each side into the area of t he
foramen beneath the centre, rendering it fiddle-shaped, but to a greater extent on the left than on the right
side; it is four lines in width where thus constricted. Its margin is separated from the infra-occipital
ridge all round by a groove, which widens below from the inclination forwards of the plane of the foramen j
its breadth is one line and one-third above mesially, and tliree hues and a half below. Tins recess lodges
the great posterior cerebellar sinus, which discharges itself by a large branch perforating the posterior
occipito-atlantal ligament, to form the bulb of the internal jugular vein.
The occipital condyle is subpedunculated; its axis is directed downwards and backwards, so that its
posterior surface, above, is nearly in the same vertical plane as the margin of the foramen magnum;
the articular surface is separated by a groove from the peduncle laterally, but is continued on it inferiorly,
indicating a considerable amount of downward flexion of the head on the neck; its form is subhemispherieal,
flattened, and notched above by the prolongation of the fossa for the medulla oblongata; its posterior surface
is marked by a faint median vertical groove; its height is three hues, and its breadth four lines.
The lateral basilar fossa presents posteriorly the shallow oval concavity for the bidb of the jugular vein;
it is most distinct on the right side; its inner angle is separated from the groove surrounding the foramen
magnum by a convex ridge, it is directed outwards and forwards to the foramen lacerum postcrius, grooving
its inner edge; and is four lines and a half long, and two and a half broad. The outer boundary of the
deep elliptic fossa, four lines and a half long and two broad, common to the posterior lacerated and carotic
foramina, is formed by the inner wall of the tympanic cavity, the lower sharp edge of which, concave inferiorly,
extends as already indicated from the paroccipital angle to the pyramidal protuberance; its inner
margin is more deeply concave than the external, thin and notched behind, thick and rounded in front.
The fossa is divided by a roughened transverse convexity, forming the floor of the vestibule leading to the
foramen ovale and f. rotundum; the foramen caroticum, transmitting the internal carotid audits accompanying
sinus, leads forwards and inwards from the anterior angle; while, from the posterior, passes upwards,
curving forwards round the vestibule just mentioned, a canal, which transmits an artery and accompanying
vein, with the glosso-pharyngeal and sympathetic nerves j its inferior orifice corresponds in part to the foramen
lacerum postcrius of mammals; its outer wall is perforated, a line above its margin, by a rounded
aperture leading to a broad groove on the base of the paroccipital process anteriorly; it transmits the
venous sinus of the membrana tympani to the internal jugular vein. The condyloid foramen for the
passage of the hypoglossal nerve, perforates the base of the peduncle of the occipital condyle, one hue and
one-third external to the foramen magnum; one line and a half from it, towards the carotic canal, is the
large aperture, transmitting the pneumogastric and spinal accessory nerves. Two minute apertures separated
by an osseous line, and probably giving exit to small venules, perforate the lower part of the interspace
between the condyloid and pneumogastric foramina on the left side; on t he right side they are a line
and a half apart.
The lateral fossa is bounded in front, by the posterior convex surface of the triangular basilar pyramid,
whose elongated inner edge extends inwards, sloping backwards to the groove, uniting the inner and anterior
angles of the fossa of each side beneath the occipital condyle. The apex and narrow outer surface are
rough : a scabrous tubercle is developed at the foot of the inner edge, separated from its fellow by a smooth
mesial notch. The breadth of t h e supra-occipital plate, between t h e mastoid notches, is two inches eight lines
and a half; from the median hue obliquely to the mastoid notch, it measures one inch eight lines and a half;
its height, mesially, is nine lines and a half; and its thickness towards the occipital ridge is five lines and a
half above, and one line and a half below. The distance between the inferior angles of the paroccipital