The =lacrimal apparatus= (Apparatus lacrimalis) comprises: (1) the
lacrimal gland, which secretes the clear lacrimal fluid; (2) the
excretory ducts of the gland; (3) the two lacrimal ducts or canaliculi,
lacrimal sac, and naso-lacrimal duct, which receive the fluid and convey
it to the nostril.
The =lacrimal gland= (Glandula lacrimalis) is situated between the
supraorbital process and the dorso-lateral surface of the eyeball (Fig.
438). It is flattened, oval in outline, and measures about two inches
(ca. 5 cm.) transversely and an inch or more (2.5 to 3 cm.) in the
sagittal direction. Its upper face is convex and is related to the
concave lower surface of the supraorbital process. The lower face is
concave in adaptation to the eyeball, from which it is separated by the
periorbita. The =excretory ducts= (Ductuli excretorii) are very small
and are twelve to sixteen in number; they open into the outer part of
the conjunctival sac along a line a little in front of the fornix
conjunctivæ superior. In appearance and structure the gland resembles
the parotid. It receives its blood-supply chiefly from the lacrimal
artery. The sensory nerve is the lacrimal, and the secretory fibers are
derived from the sympathetic.
The =puncta lacrimalia= are the entrances to the two lacrimal ducts.
Each is a fine slit-like opening (about 2 mm. long), situated close
behind the free edge of the lid and about a third of an inch (ca. 8 mm.)
from the internal canthus. The =lacrimal ducts= (Ductus lacrimales),
upper and lower, begin at the puncta and converge at the inner
commissure to open into the =lacrimal sac=. The latter (Saccus
lacrimalis) may be regarded as the dilated origin of the naso-lacrimal
duct. It occupies the funnel-like origin of the bony lacrimal canal, and
leads to the =naso-lacrimal duct= (Ductus naso-lacrimalis), which passes
forward and a little downward along the outer wall of the frontal sinus
and the nasal cavity and opens near the lower commissure of the nostril.
Its length is about ten to twelve inches (ca. 25 to 30 cm.). In the
first part of its course it is inclosed in the osseous lacrimal canal;
further forward it lies in the lacrimal groove of the maxilla, covered
at first by a plate of cartilage and then by the mucous membrane of the
middle meatus. The terminal part lies in the inferior turbinal fold and
opens on the skin of the floor of the nostril near the transition to
mucous membrane. Accessory openings may occur a little further back.
The first part of the duct, about 6 to 7 mm. in diameter, extends in a
gentle curve, convex dorsally, from the internal commissure toward a
point just above the level of the infraorbital foramen. The second
part (isthmus) is narrower (ca. 3 to 4 mm.); it extends forward and a
little ventrally about to a transverse plane through the first cheek
tooth and lies in the groove above the inferior turbinal crest. Beyond
this the duct inclines upward and widens very considerably, crosses
the nasal process of the premaxilla obliquely, and contracts at its
termination. The mucous membrane may present valvular folds, the most
distinct of which is situated at the origin.