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BONES. 95
The Inferior Border is thickened, and marked by several indentations
of a cell-like character.
The Extremities are narrowed and somewhat pointed, especially the
posterior.
Development.—The inferior turbinated l)one is developed from
cartilage from one point of ossification, which appears about the fifth
month of foetal life.

The Lachrymal Bones.
The lachrymal bones, or os unguis, two in number, are situated at the
inner and anterior portion of the orbit, just posterior to the nasal pro-
cess of the superior maxilla. They pass downward into the nasal
chamber.
The lachrymal bone (Fig. 43) is the smallest and most delicate bone
of the face. It is quadrilateral in shape, and pre-
sents two surfaces, the external or orbital and the •
internal or nasal ; and four borders, anterior, pos- ^^^^-^^
terior, superior, and inferior.
The Orbital or External Surface is divided into
two portions, an anterior and posterior, by a verti-
cal ridge of bone, the lachrymal crest.
The Anterior Portion of the orbital surface pre-
sents a smooth perpendicular groove, the lachrymal
groove, the upper part of which lodges the lachry-
mal sac. In the articulated skull this groove as-
sists in forming the lachrymal canal.
The Posterior Portion of the orbital surface is
«/"-C'^
smooth and concave, and forms part of the inner ('^ ^^ .y *" J >
wall of the orbit. The tensor tarsus muscle arises Left Lachrymal Pone, ex-
„ ,111 1 i 1 ^1 !•! terual surlace.
irom the lachrymal crest and part ot tiie orbital
surface just posterior to the crest. The hook-like process seen at the
lower portion of the lachrymal crest articulates with the lachrymal
tubercle of the superior maxilla, and completes the orbital orifice of
the lachrymal canal. Occasionally this hook-like process exists as a
separate bone known as the lesser lachrymal bone.
The Internal Surface forms part of the outer wall of the nasal cham-
ber. It is marked opposite the lachrymal crest on the external surface
by a longitudinal depression. That portion of the bone in front of this
depression enters into the formation of the outer surface of the middle
meatus of the nose ; that behind it articulates with the ethmoid bone,
and in conjunction with the superior maxilla closes the anterior ethmoi-
dal cells.
The Anterior Border is the longest of the four, and articulates at the
inner margin of the lachrymal groove with the nasal process of the
superior maxilla.
The Posterior Border is thin and uneven ; it articulates with the
anterior border of the os planum of the ethmoid bone.
The Superior Border is the thickest and shortest of the four. It
articulates with the internal angular process of the frontal bone.