On the front of the face a line drawn down from
the supraorbital notch between the bicuspid teeth to the
side of the chin will cut the exit of the second division
of the fifth nerve from the infraorbital foramen, a quarter
of an inch below the infraorbital margin, and also the exit
of the third division of the fifth at the mental foramen,
midway between the upper and lower margins of the body of the
jaw. In practice it will be found that the angle of the
mouth at rest usually corresponds to the interval between
the bicuspid teeth. The skin of the eyelids is very thin,
and is separated from the subjacent fibrous tarsal plates
by the orbicularis palpebrarum muscle. On everting the lids
the delicate conjunctival membrane is seen, and between this
and the tarsal plates lie the meibomian glands, which can
be faintly seen as yellowish streaks. From the free edges
of the eyelids come the eyelashes, between which many large
sweat- glands open, and when one of these is inflamed it
causes a "stye." Internally the two eyelids form a little
recess called the internal canthus, occupied by a small
red eminence, the caruncula lachrymalis, just external to
which a small vertical fold of conjunctiva may often be
seen, called the plica semilunaris, representing the third
eyelid of birds and many mammals. By gently drawing down
the lower eyelid the lower punctum may be seen close to the
caruncula; it is the pinhole opening into the lower of the two
canaliculi which carry away the tears to the lachrymal sac and
duct. On the side of the face the facial artery may be felt
pulsating about an inch in front of the angle of the jaw;
it runs a tortuous course to near the angle of the mouth,
the angle of the nose and the inner angle of the eye; in the
greater part of its course its vein lies some distance behind
it. The parotid gland lies between the ramus of the jaw
and the mastoid process; anteriorly it overlaps the masseter
to form the socia parotidis, and just below this its duct,
the duct of Stensen, runs forward to pierce the buccinator
and open into the mouth opposite the second upper molar
tooth. The line of this duct may be marked out by joining
the lower margin of the tragus to a point midway between
the lower limit of the nose and the mouth. The facial or
seventh nerve emerges from the skull at the stylomastoid
foramen just in front of the root of the mastoid process;
in the parotid gland it forms a network called the pes
anserinus, after which it divides into six branches which
radiate over the face to supply the muscles of expression.
Anatomy
See also face (social custom).