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AREOLAR TISSUE, TENDONS, AND MUSCLES. 173 ;

slightly outward to its insertion at the angle of the mouth. In this
position its fibres become blended with those of the orbicularis oris,
zygomaticus major and minor, and depressor anguli oris muscles.
Belations.—Its upper surface is in relation Avith the special elevator
muscle of the upper lip, the infraorbital nerve, and vessels passing
between these two muscles. At the point of its insertion it is inti-
mately adherent to the integument ; by its deep surface ^^ith the
superior maxillary bone, the buccinator muscle, and the mucous mem-
brane of the mouth.
The Riso7'ius (smiling muscle), when present, consists of a few thin
fasciculi which arise from the deep fascia covering the masseter muscle
or the parotid gland, and occasionally as far back as the mastoid pro-
cess of the temporal bone. From this point it passes transversely for-
ward and inward, its fibres becoming blended with those of tlie depressor
anguli oris and the orbicularis oris at the angle of the mouth.
The Depressor Amjull Oris (triangularis menti) is a triangular mus-
cle arising by its base from the external oblique line of the inferior
maxilla, becoming narrow as it ascends to the angle of the mouth,
where its fibres become blended with the orbicularis oris and the
other muscles of this region.
Belations.—By its superficial surface with the integument ; by its
deep surface with the Iniccinator and depressor muscles of the lip.
The Depressor Labii Inferioris (quadratus menti) is quadrilateral in
shape, and arises from the inferior maxilla by a line of attachment extend-
ing from near the symphysis to a point a little posterior to the mental
foramen. Its fibres pass upward and inward, uniting with its fellow of
the opposite side and blending with the fibres of the orbicularis oris. It
is continuous below with the platysma myoides, and above it is inserted
into the integument. Between the fibres of this muscle will be found a
considerable quantity of adipose tissue.
Relations.—By its superficial surface with a portion of the depressor
anguli oris and the integument, with which it is intimately connected
by its deep surface with the mental nerve and vessels, the mucous mem-
brane lining the lower lip, the labial glands, and the elevator muscle of
the lower lip.
The Levator Labii Inferioris (levator menti) can be best exposed by
everting the lower lip and removing the mucous membrane. It is a
small conical fasciculus arising from the upper portion of the incisor
fossa of the inferior maxilla, its fibres radiating as they pass downward
between the depressors of the lower lip to be inserted into the integu-
ment covering the chin.
Belations.—By its superficial surface with the mucous membrane of
the vestibule of the mouth, with the lower margin of the orbicularis
oris and the integument covering the chin ; by its deep surface with the
bone and the depressor muscle of the lower lip, and on its median bor-
der with its fellow of the opposite side.
The Buccinator is a thin and flat though powerful muscle situated
between the upper and lower jaws, and forming a considerable portion
of the wall of the vestibule of the mouth. Correctly speaking, it is not
a true facial muscle, belonging more properly to the pharyngeal con-