This term is usually restricted to the three pairs of large glands
situated on the sides of the face and the adjacent part of the neck—the
parotid, submaxillary, and sublingual. Their ducts open into the mouth.
The =parotid gland= (Glandula parotis) (Fig. 172)—so named from its
proximity to the ear—is the largest of the salivary glands in the horse.
It is situated chiefly in the space between the ramus of the mandible
and the wing of the atlas. It is somewhat triangular in shape, the apex
partially embracing the base of the external ear. Its length is about
eight to ten inches (ca. 20 to 25 cm.), and its average thickness nearly
an inch (ca. 2 cm.). Its average weight is about seven ounces (ca. 200
to 225 g.).
It presents for description two surfaces, two borders, a base, and an
apex. The =external= (or superficial) =surface= is covered by the
parotid fascia, the panniculus, and the parotido-auricularis muscle. It
is crossed obliquely by the jugular vein, which is embedded in the gland
tissue to a varying extent. It is also related to the great auricular
vein, the cervical branch of the facial nerve, and branches of the
second cervical nerve. The =internal= (or deep) =surface= is very
uneven, and has numerous important relations. Some of these are: the
guttural pouch, and the great cornu of the hyoid bone; the masseter,
stylo-maxillaris, digastricus, and occipito-hyoideus muscles; the
tendons of the mastoido-humeralis and sterno-cephalicus (which separate
the parotid from the underlying submaxillary gland); the external
carotid artery and some of its branches; the facial nerve; the
pharyngeal lymph glands. The =anterior= (or facial) =border= is closely
attached to the ramus of the mandible and the masseter muscle; it
overlaps the latter to a varying extent. (In some cases there is a
well-marked triangular facial process, which covers the
temporo-mandibular joint, the facial nerve, and the transverse facial
vessels.) The =posterior= (or cervical) =border= is somewhat concave,
and is loosely attached to the underlying muscles. The =base= or
=ventral border= is related to the external maxillary vein. The =apex=
is attached to the base of the external ear, which it partially
embraces.
The gland has a yellowish-gray color and is distinctly lobulated. It is
inclosed in a capsule formed by the parotid fascia. The =parotid duct=
(Ductus parotideus Stenonis) is formed at the lower part of the gland,
near the facial edge, by the union of three or four radicles. It leaves
the gland about an inch (ca. 2 to 3 cm.) above the external maxillary
vein, crosses the tendon of the sterno-cephalicus, and gains the inner
face of the pterygoideus internus. It then runs forward in the
submaxillary space below the external maxillary vein and winds around
the lower border of the mandible behind the vein, passes upward between
the vein and the masseter muscle for about two inches (ca. 5 cm.), turns
forward underneath the facial vessels, and perforates the cheek
obliquely opposite the third upper cheek tooth. Before piercing the
cheek it is somewhat dilated, but its termination is small, and is
surrounded by a circular mucous fold (Papilla salivalis).
=Blood-supply.=—Branches of the carotid and maxillary arteries.
=Nerve-supply.=—Trigeminal, facial, and sympathetic nerves.
The =submaxillary gland= (Glandula submaxillaris) is much smaller than
the parotid. It is long, narrow, and curved, the dorsal edge being
concave. It extends from the fossa below the wing of the atlas to the
body of the hyoid bone, so that it is covered partly by the parotid
gland, partly by the lower jaw. Its length is about eight to ten inches
(ca. 20 to 25 cm.), its width an inch to an inch and a half (ca. 2.5 to
3 cm.), and its thickness about half an inch (ca. 1 cm.). It weighs
about one and a half to two ounces (ca. 45 to 60 g.). It is often
divisible into two parts.
It presents for description two surfaces, two borders, and two
extremities. The =external surface= is covered by the parotid gland, the
stylo-maxillaris, digastricus, and pterygoideus internus muscles. The
tendon of the sterno-cephalicus crosses this surface, and is a useful
guide in separating the parotid gland from it. The =internal surface= is
related chiefly to the flexor muscles of the head; the guttural pouch;
the larynx; the division of the carotid artery; and the tenth, eleventh,
and sympathetic nerves. The =superior border= is concave and thin. It is
related to the guttural pouch and the duct of the gland. The =inferior
border= is convex and thicker. It is related to the thyroid gland and
the external maxillary vein. The =posterior extremity= is loosely
attached in the fossa atlantis. The =anterior extremity= lies at the
side of the root of the tongue, and is crossed externally by the
external maxillary artery.
The =submaxillary duct= (Ductus submaxillaris Whartoni) is formed by the
union of small radicles which emerge along the concave edge. It runs
forward along this border, and, after leaving the anterior extremity,
crosses the intermediate tendon of the digastricus, passes between the
hyo-glossus and mylo-hyoideus, and gains the inner surface of the
sublingual gland. Its terminal part lies on the body of the mandible,
under the mucous membrane, which it pierces opposite the canine tooth.
The orifice is at the end of a flattened papilla (Caruncula
sublingualis).
=Blood-supply.=—Occipital, external carotid, and external maxillary
arteries.
=Nerve-supply.=—Chorda tympani and sympathetic nerves.
The =sublingual gland= (Glandula sublingualis) is situated beneath the
mucous membrane of the mouth, between the body of the tongue and the
ramus of the mandible. It extends from the symphysis to the third or
fourth lower cheek tooth. Its length is about five or six inches (ca. 12
to 15 cm.) and its weight about half an ounce (ca. 15 to 16 g.).
It is flattened laterally, and has a thin =upper border= which causes an
elevation of the mucous membrane of the floor of the mouth, termed the
=sublingual crest= (Plica sublingualis). The =external surface= is
related to the mylo-hyoideus muscle, and the =internal surface= to the
genio-glossus and stylo-glossus, the submaxillary duct, and branches of
the lingual nerve. The =inferior border= is related to the genio-hyoid
muscle.
The =sublingual ducts= (Ductus sublinguales minores), about thirty in
number, are small, short, and twisted; they open on small papillæ on the
sublingual crest.
=Blood-supply.=—Sublingual artery.
=Nerve-supply.=—Trigeminal and sympathetic nerves.