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BONES. 135

the anterior apertures, and posteriorly into the pharyngeal space by the
posterior nares. Tliere are also several smaller openings leading from
the nasal fossae in other directions.
For convenience of description the nasal fossee are divided into a roof,
a floor, outer walls, and inner walls formed by the septum.
The Inner Walls or JVctsal Septum.—These are composed of six bony
structures, named in the order of their importance viz,—the perpendicular
plate of the ethmoid, the vomer, the crest of the superior maxillary and
palate bones, the rostrum of the sphenoid bone, and the nasal spine of
the frontal bone. These bones do not complete the septum, but have
a triangular notch in the anterior portion. In the recent state this is
filled by the nasal cartilage.
The nasal septum is rarely perpendicular, but is deflected either to
the one side or the other. In skulls with the flat or normal palate the
nasal septum is most apt to be jjerpendicular, but in those having the
inverted V-shai^ed (A) palate either the septum must be greatly deflected,
or pressure upward upon the vomer will push the perpendicular plate
of the ethmoid bone forward, thus causing that external protrusion
characteristic of the Roman nose.
The cause of this abnormal formation of one of these structures pari
passu with that of the other has been ascribed by Prof. Harrison Allen
to an inflammatory condition of the walls of the oro-naso-pharyngeal
space, frequent in some children, this producing tension of the muscles,
thus pressing the lateral portions inward, contracting this space, thereby
deforming the roof of the mouth,^ and changing the natural dome shape
to the gable or A shape.
The septum of the nose is also occasionally incomplete, and this
imperfection is generally situated at the junction of the perpendicular
plate of the ethmoid bone with the vomer. It is also occasionally
marked by a groove or canal on each side for the passage of the naso-
palatine nerve.
The Roof of the nasal fossa is long, narrow, and irregular in outline.
It is divided into three portions—anterior, middle, and posterior.
Tlie Anterior Portion is formed by the under surface of the nasal
bones and the nasal spine of the frontal bone. It is concave from side
to side, and extends inward and upward at an angle of about forty-
five degrees.
The Middle Portion is narrow, nearly horizontal in direction, and is
composed of the cribriform plate of the ethmoid bone.
The Posterior Portion is the longest of the three, and extends from
the posterior extremity of the cribriform plate, obliquely downward and
backward, to the free margin of the internal pterygoid plate. It is
composed of the body of the sphenoid bone and the alse of the vomer.
The Floor of the nasal fossa extends from the face anteriorly to the
pharyngeal space posteriorly. It is smooth, inclining slightly down-
ward and backward, being concave from side to side. It is composed
^ It is of great importance to recognize, and early in life gnard against, the evil
results of the inflammation of the throat in children of a strumons diathesis, since it
is. liable to produce deformity of these parts and irregularity of arrangement of the
teeth.