The =nasal cavity= (Cavum nasi) is a longitudinal passage which extends
through the upper part of the face. It is divided into right and left
halves by a median =septum nasi=. The =lateral walls= are formed by the
maxilla, premaxilla, and the perpendicular part of the palate bones.
Attached to them are the turbinal bones, which subdivide each nasal
fossa into three =meatuses= (Meatus nasi). This wall is crossed
obliquely by the =canal= and =groove= for the =naso-lacrimal duct=, and
its posterior part is perforated by the =sphenopalatine foramen=. The
=superior wall= or =roof= is formed by the frontal and nasal bones. It
is concave from side to side, and nearly straight longitudinally, except
in the posterior part, where it curves downward. It presents a median
elevation, the =nasal crest=. The =inferior wall= or =floor= is formed
by the palatine processes of the premaxillæ and maxillæ, and the
horizontal parts of the palate bones. It is wider but considerably
shorter than the roof. It is concave transversely, and nearly horizontal
from before backward, except in the posterior third, where there is a
slight declivity. The anterior part presents a median groove for the
cartilaginous septum, and a furrow for the organ of Jacobson on either
side. On either side of the palatine processes of the premaxillæ is the
=palatine cleft=.
The =septum nasi= is incomplete in the macerated skull. It is formed by
the perpendicular plate of the ethmoid behind, and the vomer below. In
the fresh state it is completed by a plate of cartilage.
The =superior meatus= (Meatus nasi superior) is a narrow passage between
the roof and the superior turbinal bone. It ends at the cribriform plate
of the ethmoid. The =middle meatus= (Meatus nasi medius) is the space
between the two turbinal bones. In its posterior part is the very narrow
opening into the maxillary sinus. The =inferior meatus= (Meatus nasi
inferior) is the channel along the floor which is overhung by the
inferior turbinal bone. It is much the largest and is the direct path
between the anterior and posterior nares.
The external aperture is bounded by the nasal bones and the premaxillæ.
[Illustration:
FIG. 37.—CROSS-SECTION OF NASAL REGION OF SKULL OF HORSE; THE SECTION
PASSES THROUGH THE ANTERIOR END OF THE FACIAL CREST, AND BETWEEN THE
THIRD AND FOURTH CHEEK TEETH.
_a_, Superior, _b_, inferior turbinal bone; _c_, _d_, cavities of _a_
and _b_; _e_, common meatus; _f_, _g_, _h_, superior, middle,
inferior meatus; _i_, _k_, passages to cavities of turbinal bones;
_l_, naso-lacrimal duct; _m_, infraorbital canal; _n_, anterior end
of maxillary sinus; _o_, septal cartilage. (After Ellenberger, in
Leisering’s Atlas.)
]
[Illustration:
FIG. 38.—CROSS-SECTION OF NASAL REGION OF SKULL OF HORSE; THE SECTION
IS CUT ABOUT HALFWAY BETWEEN THE ORBIT AND THE ANTERIOR END OF THE
FACIAL CREST, AND PASSES BETWEEN THE FIFTH AND SIXTH CHEEK TEETH.
_a_, Superior, _b_, inferior turbinal bone; _c_, _d_, cavities of _a_
and _b_; _e_, common meatus; _f_, superior, _g_, middle, _h_,
inferior meatus; _i_, placed over ridge in maxillary sinus; _k_,
communication between outer and inner (turbinal) part of maxillary
sinus; _l_, naso-maxillary opening; _m_, naso-lacrimal canal; _n_,
infraorbital canal. (After Ellenberger, in Leisering’s Atlas.)
]
The posterior extremity or fundus is separated from the cranial cavity
by the cribriform plate of the ethmoid, and is largely occupied by the
lateral masses of that bone.