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78 ANATOMY. :
crista galli are two wing-like processes of bone, the ethmoidal wings or
alae.
The posterior border of the crista galli is long, thin, and slightly
curved.
The longitudinal fold of the dura mater and the commencement of the
falx cerebri are both attached to the crista galli.
Lateral Classes (Fig. 32).—The lateral masses (ethmo-turbinated) are
cuboidal in form and present six surfaces—the superior and inferior,
,. „., external and internal, anterior
'
hio. 32. , ^ .
and posterior.
—
The Superior Surface.
The anterior portion is com-
posed of irregular cell-like
openings, which are covered
in and completed by articu-
lation with the frontal bone.
The Ethmoidal Foramina
(Tnternal Orbital Canals).—
Crossing this border, about
half an inch apart, are two
slight grooves, which, when
Ethmoid Bone, inner surface of right lateral mass (enlarged).
conjoined to similar grooves
on the external border of the ethmoidal notch of the frontal bone, form
the anterior and posterior ethmoidal foramina : the first transmits the
internal nasal nerve, a branch of the ophthalmic and anterior ethmoidal
vessels, the posterior transmitting the posterior ethmoidal vessels and
spheno-ethmoidal nerve, a branch of tlie nasal.
The Inferior Surface extends from the inferior external border of the
lateral mass to the free margin of the middle turbinated bone in the
articulated skull, and from the anterior to the posterior surface of the
lateral mass. It is divided into three portions
(a) The external portion lies b(4^veen the inferior external border of
the lateral mass and the uncinate process anteriorly, the middle and pos-
terior lino being formed by a curved plate of bone in the median line of
the inferior surface of the external mass. This portion articulates with
the superior border of the nasal surface of the superior maxilla, closing
in the cell-like cavities found on that border.
(6) Anteriorly, the middle jiortion is formed by the uncinate process
and posteriorly by the curved plate of bone forming the internal wall of
the anterior ethmoidal cells. The uncinate process arises from the mid-
dle of the anterior surface of the ethmoid bone, and extends downward,
outward, and backward, being somewhat hook-shaped in outline. It
articulates with tlie inner surface of the nasal process of the superior
maxilla, the ethmoidal process of the inner surface of the lachrymal
bone, and the infeiior tuil>iiiated bone; it also assists in closing the
orifice leading to the ma.xillarv sinus.
(c) The internal j)ortioii is free, and is formed by the curved border
of the middle turbinated bone in the articulated skull.
The Internal or Nasal Surface is the mo.'^t complex portion of the
bone. It forms part of the external wall of the nasal chamber, or all