Base Of The External Surface.
External to the
stylo-mastoid foramen is the auricular fissure, for the auricular branch
of the pneumogastric, bounded behind by the mastoid process. Upon the inner
side of the mastoid process is a deep groove, the digastric fossa; and
a little more internally the occipital groove, for the occipital artery.
At the base of the internal pterygoid plate is a large and somewhat triangular
aperture, the foramen lacerum medium, bounded
in front by the great wing of the sphenoid, behind by the apex of the petrous
portion of the temporal bone, and internally by the body of the sphenoid and
basilar process of the occipital bone: it presents in front the posterior
orifice of the Vidian canal; behind, the aperture of the carotid canal. The
basilar surface of this opening is filled in the recent state by
fibro-cartilaginous substance f across its upper or cerebral aspect passes the
internal carotid artery. External to this aperture the petro-sphenoidal
suture is observed, at the outer termination of which is seen the orifice
of the canal for the Eustachian tube and tLat for the Tensor tympani muscle.
Behind this suture is seen the under surface of the petrous portion of the
temporal bone, presenting, from within outward, the quadrilateral, rough
surface, part of which affords attachment to the Levator palati and Tensor
tympani muscles; external to this surface the orifices (If the carotid canal
and the aqureductus cochlere, the former transmitting the internal carotid
artery and the ascending branches of the superior cervical ganglion of the
sympathetic, the latter serving for the passage of a small artery and vein to
the cochlea. Behind the carotid canal is a large aperture, the Jugular
foramen. formed in front by the petrous portion of the temporal, and
behind by the occipital; it is generally larger on the right than on the left
side, and is divided into three compartments by processes of dura mater. The
anterior is for the passage of the inferior petrosal sinus; the posterior, for
the lateral sinus and some meningeal branches from the occipital and ascending
pharyngeal arteries; the central one, for the glosso-pharyngeal,
pneumogastric, and spinal accessory nerves. On the
ridge of bone dividing the carotid canal from the jugular foramen is the small
fora.men for the transmission of Jacobson's nerve; and on the wall of the
jugular foramen, near the root of the styloid process, is the small aperture
for the transmission of Arnold's nerve.
