This artery (A. maxillaris interna) is much the larger of the two
terminal branches of the external carotid. It begins at the inner side
of the posterior border of the mandible about two inches (ca. 5 cm.)
below the articulation of the jaw and ends in the anterior part of the
pterygo-palatine fossa. On account of its complex course and the large
number of branches given off it is convenient to divide it into three
parts.
The =first part= is much the longest, forms an =S=-shaped curve, and is
in great part in contact with the guttural pouch. It passes upward and
forward on the inner surface of the mandible a distance of about an inch
(ca. 2 to 3 cm.) and is related here to the vein, which is ventral. It
then turns inward below the external pterygoid muscle and the inferior
maxillary nerve, passes between that muscle and the tensor palati, and
runs forward to enter the alar (pterygoid) foramen. This part gives off
the following branches:
1. The =inferior alveolar= or =dental artery= (A. alveolaris mandibulæ
s. inferior) passes downward and forward with the homonymous vein and
nerve, being at first between the external and internal pterygoid
muscles, then between the latter and the ramus of the mandible. It
enters the mandibular foramen, passes downward and forward in the
mandibular canal, and terminates at the mental foramen by dividing into
mental and incisor branches. The =mental branch= (A. mentalis) emerges
through the mental foramen and anastomoses in the lower lip with the
opposite artery and the inferior labial. The =incisor branch= continues
forward in the bone, supplies twigs to the canine and incisor teeth, and
anastomoses with its fellow of the opposite side. Collateral branches
are detached to the pterygoid and mylo-hyoid muscles, and within the
bone to the teeth, alveolar periosteum, the gums, and the spongy
substance of the mandible.
2. The =pterygoid arteries=, two or three in number, are distributed to
the pterygoid and tensor and levator palati muscles.
3. The =tympanic artery= is a very small vessel which passes along the
Eustachian tube to the petro-tympanic fissure (of Glaser) and enters the
middle ear.
[Illustration: