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BONES. 79
that portion of the wall which is devoted to olfaction. It commences at
the cribriform plate and descends downward and slightly forward. Its
posterior two-thirds is divided by a sulcus, which is directed backward
and inward. This groove forms the superior meatus of the nose. It
extends backward to the posterior margin of the bone and terminates in
a deep notch. The anterior third of the internal surface is uninterrupted
from the cribriform plate to its lower border.
The Superior Meatus divides the internal surface of the lateral mass
into two portions—the superior and middle turbinated bones it extends
;
antero-posteriorly upward, outward, and forward from the median line,
and communicates with the ethmoidal cells.
The Superior Turbinated Bone is all that portion between the sulcus
and the cribriform plate.
The Middle Turhinated, Bone is that portion of the internal surface
lying below the sulcus and between it and the lower free border. The
middle turbinated bone is free, and extends downward into the nasal
chamber. Its lower border curves outward and upward toward the
superior maxilla, the outer surface of the curve appearing like a scroll.
This bone overhangs the middle meatus of the nose.
The Infundibuluni.—At the anterior portion of the middle meatus
may be seen a passage known as the infundibuluni, leading up through
the anterior ethmoidal cells into the frontal sinus.
The External or Orbited Surface of each lateral mass is a thin, smooth
lamina of bone, quadrilateral in form. Its length from the front to the
back is about double its width. This surface has also received the name
" OS planum," on account of its smoothness ; it forms part of the inner
wall of the orbit. The two grooves which in the articulated bone assist
in forming the anterior and posterior ethmoidal foramina indent the
superior edge of this surface, M-hich articulates with the frontal bone.
The inferior edge articulates with the superior maxilla.
The Anterior Surface extends inwardly from the os planum until it
reaches the nasal surface of the bone. It presents numerous cell-like
depressions. The inner portion of the anterior surface articulates with
the nasal process of the superior maxilla, the internal portion being
covered by the lachrymal bone ; this, with the aid of the frontal bone,
already referred to, completes the anterior ethmoidal cells.
The Posterior Surface of the lateral masses is thin and penetrated by
numerous openings. It is divided into two portions, a superior and an
inferior. The superior portion articulates with the turbinated plates of
the sphenoid bone, and the inferior portion with the orbital process of
the palate bone. These bones conjointly complete the posterior ethmoid
cells.
The Cribriform Plate is symmetrical in outline, being divided into two
lateral halves by the crista galli. It forms part of the base of the ante-
rior fossa of the brain-case, and fits the ethmoidal notch of the frontal
bone. It unites the two lateral masses and vertical plate of the bone. The
olfactory sulcus, for the lodgment of the olfactory bulbs of the brain,
are depressions of the cribriform plate situated on each side of the crista
galli. This plate is pierced by numerous foramina for the transmission
of the filaments of the olfactory nei'ves : those next the crista galli pass