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194 ANAT03IY.

between the middle and inferior constrictors on its way to the thyro-
hyoid membrane. The internal surface where it does not overlap the
superior muscle is covered by mucous membrane and the stylo-pharyn-
geus and the palato-pharyngeus muscles.
Nerves.—The nerve-supply is from the pharyngeal plexus.
Actions.—The upper fibres assist in elevating the hyoid bone and all
the structures connected with it ; it also draws forward the posterior
pharyngeal wall.
The Inferior Constrictor muscle of the pharynx is the broadest, thick-
est, and shortest of the three, and lies the most superficially. As its
name implies, it is at the lower or inferior portion of the pharynx. It
arises from various points, commencing below at the lower and posterior
part of the ci icoid cartilage, and from a tendinous arch between the cri-
coid and thyroid cartilages, from the inferior cornu and the oblique line
and upper border of the thyroid cartilage. From these points of origin the
fibres pass backward and upward, and, curving inward, join the raphe
and the fibres of its fellow from, the opposite side. The fibres of the
lower portion are the shortest ; their direction is horizontal, and they
combine with those of the oesophagus without a line of demarcation.
The balance of the fibres are about one-eighth of an inch below the
basilar process, and pass upward and backward, with an increase of
obliquity, to the posterior median line of the pharynx, covering more
than half its length.
Variations.—The muscle sometimes receives a fasciculus from the
thyro-hyoid, crico-thyroid, and sterno-thyroid muscles, or even from
the trachea.
Relations.—The external surface posteriorly is in apposition with the
cervical vertebrae and the muscles of this region ; laterally with the
thyroid gland, the carotid arteries, and the sterno-hyoid muscles, the
internal surface of the middle constrictor, the stylo-pharyngeus, and the
palato-pharyngeus muscles, also the mucous membrane of the pharynx.
The superior laryngeal nerve and vessels pass over the upper border to
the larynx, and the inferior ascend beneath its lower border.
Nerves.—The muscle is supplied by the pharyngeal plexus and the
external laryngeal nerve.
Actions.—It assists in propelling the bolus of food into the oesophagus,
reduces the size of the lower part of the pharynx, and can act independ-
ently of the other muscles of the set.
The Stijlo-pharyngeus muscle is slender, though the largest and longest
of the styloid set : above it is round ; below it is broad and thin. It
arises from the inner side and near the base of the styloid process, passes
downward and inward Ijotween the superior and middle constrictors of
the pharynx, and gradually expands under tlie mucous membrane, some
of its fibres being inserted into the lateral walls of the pharynx and
united with the palato-pharyngeus : these are inserted into the posterior
border of the thyroid cartilage.
The glosso-pharyngeal nerve accompanies this muscle, commencing
on the outer side, and crosses over on its way to the tongue.
Variations.—Cleavage or doubling of the stylo-pharyngeus muscle
is frequent ; occasionally it has been found divided into three. Super-