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136 : ANAT03IY.

of that portion of the bony strncture of this region which forms the
premaxillse and the palatal processes of the superior maxillae and hori-
zontal plates of the palate bones.
The External or Lateral Wall is the most extended, uneven, and com-
plicated portion of the nasal fossa. Seven bones enter into the forma-
tion on each side—viz. the nasal, superior maxilla, lachrymal, ethmoid,
inferior turbinated, and palate bones, and the pterygoid process of the
sphenoid bone. To form the outer walls of both sides twelve bones are
required—two of the brain-case, the ethmoid and the sphenoid, and all
the bones of the face excepting four, the malar, the vomer, and the
inferior maxilla. These walls are divided by the projections of the tur-
binated processes of the ethmoid bone and the inferior turbinated bone
into three horizontal compartments, the superior, middle, and inferior.
The Superior Jleatus is the shortest and shalloM'est of the three. It
is situated between the superior and inferior turbinated masses of the
ethmoid bone, and in the articulated skull between the superior and
inferior turbinated bones. •
The Middle 3Ieatus is situated between the middle and inferior tur-
binated bones, and forms two-thirds of the posterior portion of the outer
wall of the nasal fossa.
The Inferior Meatus is situated between the inferior turbinated bone
and the floor of the nose. It is the longest of the three meati.
The openings into the nasal fossa are numerous, and may be classified
as follows
The Anterior Aperture is that pyriform opening leading from the
face into the fossa, and has been previously described.
The Posterior Aperture opens into the pharyngeal space. It is
bounded above by the vaginal process of the sphenoid bone and the
alse of the vomer; below by the palatal process of the palate bone;
internally by the vomer; and externally by the free border of the inter-
nal plate of the pterygoid process of the sphenoid bone.
The Lachrymal Canal ojjens into the superior portion of the inferior
meatus, behind the nasal process of the superior maxilla and external
to the inferior turbinated bone. This canal is occupied by the nasal or
lachrymal duct, which conveys the lachrymal fluid froni the eye into
the nose.
The Spheno-palatine Foramen is situated in a line just back of the
superior meatus. It is bounded below by the palate bone, above by
the sphenoid bone, and opens into the spheno-palatine space. It trans-
mits into the nasal fossa the naso-palatine nerves and vessels.
The Incisor Foramen, or Foramen of Stenson, is situated in the
anterior portion of the nasal fossa, near the septum and back of the
premaxilla. It opens into the anterior palatine canal on the oral aspect
of the hard palate, and transmits the anterior palatine vessels.
The Foramen of Scarpa is situated within the intermaxillary suture,
and opens into the anterior jxilatine canal on the oral aspect of the hard
palate. It transmits the naso-palatine nerve.
The Olfactory Apertures are those numerous small openings found in
the cribriform plate of the ethmoid bone. They communicate with the
brain-case, and transmit the filaments of the olfactory nerves.