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BLOOD-VESSEL SYSTEM OF THE HEAD, ETC. 237

situatt'd in the neck, the parotid gland, the styloid process, and stylo-
pharyngeus muscle being to its outer side. Its deep relations are with
the tonsils, the superior constrictor muscle separating them, the -walls of
the pharynx, and transverse process of the upper three cervical vertebrae,
the rectus capitis anticus major muscle being posterior to it. The artery
is enclosed in a sheath in company M'ith the internal jugular vein and
pneumogastric nerve, the vein lying upon the outer side posterior to the
artery. Upon reaching the skull the vein separates from the artery
and passes through the jugular or posterior lacerated foramen, the
artery passing through the carotid foramen. The glosso-pharyngeal,
pneumogastric, spinal accessory, and hypoglossal nerves are situated be-
tween the two vessels near these foramina. The occipital and posterior
auricular arteries cross it on the outside, the former below the digastric
muscle, the latter above. The pneumogastric nerve and the upper cer-
vical ganglion of the sympathetic are deeper than, and situated posterior
to, the vessel. The hypoglossal nerve crosses to its outer side, near the
lower margin of the digastric muscle ; the glosso-pharyngeal nerve and
pharyngeal branch of the pneumogastric pass between the external and
internal carotids. The superior and external laryngeal nerves are inter-
nal to both arteries.
The cervical portion of the internal carotid seldom gives off any
branches, though occasionally its lower portion supplies the occipital or
ascending pharyngeal arteries. These, however, are rare variations.
The Petrous Portion of the internal carotid enters the carotid foramen
on the under surface of the temporal bone, and passes through a canal
to a point where it enters the cavernous sinus within the brain-case.
Its course within the bone is at first upward, passing immediately in
front of the tympanum or middle ear and the internal ear, being sepa-
rated from them by a thin lamina of bone. It then passes horizontally
forward and inward to the middle lacerated foramen, extending across
the tissues filling in this aperture.
This portion of the artery gives off a small branch to the tympanum
which anastomoses with tympanic branches from divisions of the exter-
nal carotid.
The Chvcrnous Portion of the internal carotid commencies immedi-
ately above the middle lacerated foramen, and passes upward to and
along the sigmoid groove on the lateral surface of the body of the sphe-
noid bone. It terminates in the intracranial portion of the artery by
passing through the upper wall (which is membranous) of the cavernous
sinus close to the anterior clinoid process. The artery is situated on the
inner portion of the cavernous sinus. It is surrounded by filaments of
the sympathetic nerve, and is accompanied by the sixth nerve, which is
situated to its outer side. These structures are all covered by an envelope
derived from the lining membrane of the sinus. The third, fourth, and
oplithalmic nerves pass through the sinus external to the envelope.
Branches of this portion of the artery are distributed to the dura
mater, the pituitary body, Gasserian ganglion, and the walls of the
cavernous and inferior petrosal sinuses. It also gives off a branch
which anastomoses with the middle meningeal artery.
The Intracranial Portion of the internal carotid commences after the