_1_, Nasal bone; _2_, tendon of levator labii superioris proprius;
_3_, external nasal nerve; _4_, nasal diverticulum; _5_, outer wall
of _4_; _6_, dilatator naris inferior; _7_, levator nasolabialis +
dilatator naris lateralis; _8_, maxilla and premaxilla; _9_,
naso-lacrimal duct; _10_, _11_, chief branches of superior labial
nerve, with superior labial artery at their inner side; _12_, nasal
cavity; _13_, superior turbinal fold; _14_, inferior turbinal fold,
inclosing cartilaginous prolongation of inferior turbinal bone;
_15_, venous plexus; _16_, septum nasi; _16′_, parietal cartilage;
_17_, vomero-nasal organ (of Jacobson); _18_, venous plexus of
palate; _19_, buccinator; _20_, skin; _23_, anterior nasal nerve;
_24_, palatine process of premaxilla. (After Ellenberger-Baum, Top.
Anat. d. Pferdes.)
]
The muscles of the nostrils have been described.
=Blood-supply.=—Palato-labial, superior labial, and lateral nasal
arteries.
=Nerve-supply.=—Trigeminal and facial nerves.
The nasal cavity is divided into two symmetrical halves by the median
=septum nasi=. The osseous part of the septum (Septum osseum) is formed
behind by the perpendicular plate of the ethmoid and below by the vomer.
A few ridges on the former correspond to the ethmoidal meatuses. The
major part of it, however, is formed by the =septal cartilage=
(Cartilago septi nasi). The surfaces of the cartilage are marked by
faint grooves for the vessels and nerves which course over it. The
=dorsal border= is attached along the frontal and nasal sutures, and
extends beyond the apices of the nasal bones about two inches (ca. 5
cm.). From this border a thin, narrow plate, the =parietal cartilage=
(Cartilago parietalis) curves outward for a short distance on either
side. Near the nostrils these plates are somewhat wider, partially
making good the defect in the bony roof of the cavity in this situation.
The =ventral border= is thick and rounded; it lies chiefly in the groove
of the vomer, but anteriorly it occupies the space between the
premaxillary bones. The =posterior border= is continuous with the
perpendicular plate of the ethmoid bone.[121] The alar cartilages are
attached to the anterior extremity by fibrous tissue in such a manner as
to allow very free movement—in fact, an actual joint may be found. The
ventral part of the cartilage is about half an inch (ca. 1 cm.), the
middle part about one-tenth of an inch (ca. 2.5 mm.), and the dorsal
part about a quarter to a third of an inch (ca. 6 to 8 mm.) in
thickness.
[Illustration:
FIG. 346.—NASAL CARTILAGES OF HORSE, DORSAL VIEW. (After
Ellenberger-Baum, Anat. für Künstler.)
]
The two =turbinal bones= (Conchæ nasales) project from the lateral wall,
and divide the outer part of the cavity into three =meatuses=—superior,
middle, and inferior.
The =superior meatus= (Meatus nasi dorsalis) is a narrow passage,
bounded dorsally by the roof of the cavity, and ventrally by the
superior turbinal bone; its posterior end is closed by the junction of
the inner plate of the frontal bone with the cribriform plate and
lateral mass of the ethmoid. It transmits air to the upper part of the
olfactory region.
[Illustration: