_a_, _a′_, Dilatator naris transversus; _b_, levator labii superioris
proprius; _b′_, tendon of _b_; _b″_, common tendon of two levatores
labii superioris proprii; _c_, _c′_, dilatator naris inferior; _d_,
_e_, dilatator naris superior; _f_, orbicularis oris; _g_, levator
nasolabialis, a portion of which is removed; _h_, dilatator naris
lateralis (cut); _i_, cornu of alar cartilage; _k_, nostril; _k′_,
false nostril; _l_, nasal diverticulum; _m_, nasal bone. (After
Ellenberger-Baum, Top. Anat. d. Pferdes.)
]
_Action._—To dilate the nostril.
_Structure._—The muscle has a flat tendon of origin, passes between the
two branches of the levator nasolabialis, and spreads out in the
external wing of the nostril. The lower fibers blend with the
orbicularis oris.
_Relations._—Superficially, the skin, fascia, and the labial branch of
the levator nasolabialis; deeply, the maxilla and the nasal branch of
the levator nasolabialis.
_Blood-supply._—Facial artery.
_Nerve-supply._—Facial nerve.
3. =Dilatator naris transversus= (M. transversus nasi).—This is an
unpaired, quadrilateral muscle, which lies between the nostrils. It
consists of two layers.
_Attachments._—Superficial layer, the superficial faces of the laminæ of
the alar cartilages; deep layer, the convex edges of the cornua of the
same.
_Action._—To dilate the nostrils.
_Structure._—It is composed of transverse fleshy fibers, which blend
below with the orbicularis.
_Relations._—Superficially, the skin, fascia, and tendinous expansion of
the levator labii superioris proprius; deeply, the alar cartilages, the
extremity of the septum nasi, and the palato-labial artery.
_Blood-supply._—Palato-labial artery.
_Nerve-supply._—Facial nerve.
4. =Dilatator naris superior= (Pars dorsalis m. lateralis nasi).—This
very thin muscle occupies the angle between the nasal process of the
premaxilla and the nasal bone.
_Origin._—The lateral border of the nasal bone.
_Insertion._—The inner wall of the false nostril and the parietal lamina
of the septal cartilage.
_Action._—To dilate the vestibule of the nasal cavity.
_Structure._—Fleshy.
_Relations._—Superficially, the skin, fascia, and levator labii
superioris proprius; deeply, the parietal cartilage and false nostril.
_Blood-supply._—Facial artery.
_Nerve-supply._—Facial nerve.
5. =Dilatator naris inferior= (Pars ventralis m. lateralis nasi).—This
is a similar but thicker muscle, which lies on the nasal process of the
premaxilla.
_Origin._—The maxilla and the nasal process of the premaxilla.
_Insertion._—The cartilaginous prolongations of the turbinal bones and
the inner wall of the false nostril.
_Action._—To rotate the turbinal outward and dilate the nostril and the
vestibule of the nasal cavity.
_Structure._—Fleshy. A division into two or more parts may be
recognized. A small part posteriorly is inserted into the cartilage of
the dorsal turbinal bone, while the bulk of the muscle is inserted into
the cartilage of the ventral turbinal bone. A few fibers also pass
between the cornu of the alar cartilage and the outer wing of the
nostril.
_Relations._—Superficially, the levator labii superioris proprius, the
levator nasolabialis, and the lateral nasal artery; deeply, the maxilla,
the premaxilla, and the anterior nasal branch of the infraorbital nerve.
_Blood-supply._—Facial artery.
_Nerve-supply._—Facial nerve.