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5b. 3. The Lacrimal Bone
FIG. 163 - Left lacrimal bone. Orbital surface. Enlarged. (Os Lacrimale)
The lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit (Fig. 164). It has two surfaces and four borders.Surfaces.—The lateral or orbital surface (Fig. 163) is divided by a vertical ridge, the posterior lacrimal crest, into two parts. In front of this crest is a longitudinal groove, the lacrimal sulcus (sulcus lacrimalis), the inner margin of which unites with the frontal process of the maxilla, and the lacrimal fossa is thus completed. The upper part of this fossa lodges the lacrimal sac, the lower part, the naso-lacrimal duct. The portion behind the crest is smooth, and forms part of the medial wall of the orbit. The crest, with a part of the orbital surface immediately behind it, gives origin to the lacrimal part of the Orbicularis oculi and ends below in a small, hook-like projection, the lacrimal hamulus, which articulates with the lacrimal tubercle of the maxilla, and completes the upper orifice of the lacrimal canal; it sometimes exists as a separate piece, and is then called the lesser lacrimal bone. The medial or nasal surface presents a longitudinal furrow, corresponding to the crest on the lateral surface. The area in front of this furrow forms part of the middle meatus of the nose; that behind it articulates with the ethmoid, and completes some of the anterior ethmoidal cells. Borders.—Of the four borders the anterior articulates with the frontal process of the maxilla; the posterior with the lamina papyracea of the ethmoid; the superior with the frontal bone. The inferior is divided by the lower edge of the posterior lacrimal crest into two parts: the posterior part articulates with the orbital plate of the maxilla; the anterior is prolonged downward as the descending process, which articulates with the lacrimal process of the inferior nasal concha, and assists in forming the canal for the nasolacrimal duct. Ossification.—The lacrimal is ossified from a single center, which appears about the twelfth week in the membrane covering the cartilaginous nasal capsule. Articulations.—The lacrimal articulates with four bones: two of the cranium, the frontal and ethmoid, and two of the face, the maxilla and the inferior nasal concha.
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