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BLOOD-VESSEL SYSTEM OF THE HEAD, ETC. 235

The Vidian Branch passes backward in the Vidian canal in the oppo-
site direction to the A'idian nerve. Its branches are distributed to the
upper part of the pharynx, the opening of the Eustachian tube, the
levator palati muscle, and to the tympanum. It anastomoses with the
ascending pharyngeal and stylo-mastoid arteries.
The Fterygo-palatine Branch is a small artery which passes back-
ward and downward in the pterygo-palatine canal, accompanied by the
pharyngeal nerve. It is distributed to the sphenoidal cells, Eustachian
tube, and upper part of the pharynx.
The Nasal or >Spheno-palatine Branch may be considered as the ter-
minal of the internal maxillary artery. It passes in a forward direction,
entering the nasal chamber through the spheno-palatine foramen, which
is situated at the back part of the superior meatus, dividing into inter-
nal and external branches. The internal division is the continuation
of the spheno-palatine, and holds the same name, though sometimes
it is called the artery of the septum, as it runs downward and forward
in the groove of the vomer, and terminates by anastomosing with the
descending palatine artery at the incisive foramen. It is distributed to
the bone, cartilage, and mucous membrane of the nasal septum. The
external branches, several in number, are distributed to the lateral part
of the nose, including the ethmoidal and sphenoidal cells, the maxillary
sinus, and the mucous membrane covering these parts.
Variations.—The internal maxillary artery seldom varies in its origin,
though it has been known to arise from the facial (Quain). The num-
ber of branches given off may vary, there being two or more, which
arise by one common trunk. The branches may also convey blood to
parts which are generally supplied by the facial and lingual, and by the
branches of the ophthalmic and the temporal arteries. In the same
way the cranial branches may interchange with those of the internal
carotid.

The Internal Carotid Artery.
The Internal Carotid Artery (Fig. 110) is about 6 mm, (l inch) in
calibre, and, as its name indicates^ is distributed in great ]iart to the
internal, middle, and anterior structures of the brain-case. It also sup-
plies the eye and the parts within the orbit, and partially the nasal
chamber, forehead, and nose. It is one of the terminal branches of
•
the conmion carotid, arising from that artery at its bifurcation opposite
the superior border of the thyroid cartilage, from which point it passes
upward, generally with a slight curve, to the carotid foramen in the
petrous portion of the temporal bone.
The internal carotid artery is divided anatomically into four portions
—cervical, petrous, cavernous, and intracranial.
The Cervical Portion is situated within the neck, extending from the
origin of the internal carotid in the superior carotid triangle to the caro-
tid foramen. Its line is usually slightly curved, though almost vertical,
but in some cases it will be found to be quite tortuous.
Bekdions.—At first it is located more superficially than the external
carotid, and a little posterior to its outer side. It is covered by the