The triangular surface for the attachment of the M. Levator ossis quadrati, occupies the digital fossa,
extending round the posterior border of the foramen opticum; it is prolonged outwards over the tympanic
convexity, surrounded by a smooth depressed marginal tract of the latter, corresponding to a vascular
circle. The irregular tympanic excavation is bounded above by the mastoid, and beliind by the paroccipital
process. The post-temporal process of the mastoid is formed by a thick quadrantal plate projecting
outwards with an inclination forwards, beliind the temporal fossa; its outer edge is rough, and gives
attaclunent to t he external mandibular ligament, and viewed laterally projects downwards and forwards like
a styloid process in front of the articular cavity for the anterior superior condyle of the tympanic. This
cavity impresses the base and posterior surface of the post-temporal plate, thinning it internally; its anteroposterior
and transverse diameters, are three lines and a half. The mastoid process is a longitudinally
extended, low, obtuse and thick pyramidal plate, projecting downwards so as to conceal the large quadrate
superior pneumatic foramen, iuternal to it and between the tympanic articular cavities; its external smooth
facet is separated by a slight ridge from the small posterior one, which is grooved at its base, and separated
by a notch from the paroccipital process; its inner surface is reticulate, and forms with the external a sharp
edge. The inferior articular facet for the reception of the postero-superior condyle of the tympanic is
oblong, three lines and two thirds long and two lines and two tliirds deep, and composed of a smaller inner
and a larger posterior segment, at right angles to each other; beneath its anterior extremity is the external
lacerated wall of a canal which ascends from the foramen lacerum posterius, curving forwards round the
tympanic tube; it passes into a groove, arching backwards to the lower angle of the upper pneumatic orifice,
and terminating in a narrow canal which traverses the diploe at the floor of that orifice, emerges at the
canalicular convexity on the occipital aspect. The paroccipital process presents a shallow groove at its
base anteriorly, which widens as it ascends; its floor is cellular above, behind the inferior tympanic facet;
below it curves inwards, and passes into a rounded orifice which perforates the outer wall of the canal
just mentioned ; the groove lodges the sinus of the membrana tympani, which transmits its blood to the
internal jugular vein; its outer edge is undefined, the inner is sharp and gives attachment to the membrana
tympani.
Internal to it is a shorter but deeper concavity, also exposing pneumatic cells beneath the inferior
tympanic facet. In the mouth of the tympanic tube is seen posteriorly the vertically oval orifice of a
short canal, leading inwards and slightly forwards to the foramina ovale and rotundum of the vestibule,
which are separated by an oblique grooved bar; in front of it, is a large pneumatic orifice transmitting air
to the diploe surrounding the labyrinth, and the oval orifice of the depressed basilar efferent pneumatic
canal, passing forwards and inwards separated by a thin septum from the wide Eustachian tube: the
efferent apertures from which open into the cells of the basilar protuberance, over which it passes converging
to its fellow; the common orifice has already been described. The anterior wall of the tympanic
tube is perforated by an aperture leading into the pneumatic canal. From the supra-orbital to the mastoid
notch is two inches four lines and a half; between the opposite surfaces of the prefrontal, and of the
paroccipital process inferiorly, is an interval of two inches; the anterior margin of the orbit is one inch six
lines and a half deep, and from the temporal notch to the lower angle of the paroccipital, one inch five lines
and a half.
The broad superior facet of the cranium, on the removal of the beak so as to expose the upper surface
of the turbinated ala: of the ethmoid, presents a subhexagonal figure; the anterior border, corresponding
to a line drawn between the anterior angles of the prefrontals, being only one half of the width of the
posterior; and the antero-lateral margins about twice as long as the postero-latcral: behind the line of the
polished elevated area of the orbital fossa, the posterior rounded edge of which forms its anterior margin,
which is seven lines long; its base is 'four lines and one-third; for a hue above it, t he surface is, as it were,
scooped out.
A smooth tract, corresponding to the post-orbital vascular flexus, and leading to the foramen rotundoovale,
occupies the remainder of the floor of the temporal fossa: it terminates below, at the convex projection
of the tympanic tube, which runs horizontally outwards and backwards; its anterior wall is formed
by a curved plate, which, after covering the iiiferior efferent pneumatic cells and the Eustachian tube, is
attached to the outer margin of the sphenoid lozenge and basilar protuberance; behind which, it presents
a deep triangular incision, bounded below by the thin, inferiorlv concave edge; formed by its junction, at an
acute angle, with the inner wall. Its orifice is in a hue with the post-temporal process; the edge is deeply
concave, the lower angle being prolonged into a sharp, slightly incurved styloid process. The tympanic
convexity subsides internally towards the digital fossa, which is the deepest part of the lateral facet, containing
in front the optic foramen, and behind, the subdivisions of the foramen lacerum animus, perforating
the thinnest part of the cranial parietes. The foramen for the transmission of the oculomotor and abducens
nerves, occurs immediately behind the lower moiety of t he optic foramen; it is longitudinally oval, one line
and a half long, and one line high; it is directed obliquely upwards, and divided internally into three apertures
by delicate osseous threads: the posterior one is the orifice of a canal, four lines and a half long,
which lodges the sixth nerve; the two anterior give passage to the divisions of the third pair, and run into
a vertical groove separated by a ridge from that which is continued upwards from the posterior orifice, both
terminate on a level with the upper margin of the foramen opticum; at the apex of the anterior is situated the
minute orifice of a canal, two lines long, for the transmission of the patheticus nerve; it is capable of admitting
a fine bristle; a groove passes forwards and upwards from it. At t he lower angle, between the optic foramen
and that for the third nerve, is the aperture of a very slender canal, opening internally into the sella turcica,
and probably conducting outwards, a twig from the ento-carotid artery. Above the tympanic convexity,
and three lines and a half from the posterior border of the foramen opticum, is the rounded, sharp-edged
aperture, one line in diameter, for t he transmission of the ophthalmic branch of the trigeminal nerve; a
groove, concave downwards, leads forwards across the patheticus foramen, and apparently enters the optic
outlet, behind the supra-orbital furrow. The vertically oval orifice, foramen rolundo-ovale, giving passageto
the second and third divisions of the fifth pair, occurs midway between it and the margin of the osseous
tympanic aperture; it is one line and a half high, and one wide; an osseous thread separates from its base
anteriorly, a minute foramen.
The digital fossa is separated by a slight ridge from a concavity on the side of the most constricted
part of the sphenoid, beneath the foramen opticum; this depression is produced by the great trunk of the
internal maxillary vein, it slopes inwards below, and is separated from its fellow by the narrow, sharp-edged
gutter on t he inferior surface, leading to the common orifice of the Eustachian tubes; its superior border is
convex upwards; in the posterior triangular tract between it, and the edge of the digital fossa, are two
foramina; the anterior and upper is the smallest, and longitudinally oval; the posterior and larger has the
same shape, but its greatest diameter is at right angles to that of the former. A narrow band, one line in
breadth, separates them, and presents two capillary apertures above, but supports below the minute, thin
and flexible upwardly-curved style, representing the articular peduncle for the pterygoid; which does not exist
on the right side. These foramina transmit communicating branches from the internal maxillary artery to the
ento-carotid, with their accompanying venous sinuses; the canals to which they lead pass backwards in the
septum between the Eustachian tube and the efferent pneumatic cells, and open into the carotid canal as it
curves inwards to unite with its fellow.