Lacrimal Bones
The lacrimal bones, the smallest and most fragile of the cranial bones are situated at the front parts of the medial walls of the orbits (figs. 376. 336). Each lacrimal bone has two surfaces and four borders. The lateral or orbital surface (fig. 374) is divided by a vertical ridge termed the crest of the lacrimal bone (posterior lacrimal crest). In front of this crest there is a vertical groove, the anterior border of which articulates with the posterior border of the frontal process of the maxilla to complete the lacrimal groove for the lodgment of the lacrimal sac. The medial wall of the groove is prolonged downwards to assist in forming the bony canal for the nasolacrimal duet by articulating with the lips of the nasolacrimal groove of the maxilla, and with the lacrimal process of the inferior nasal concha. The portion behind the crest is smooth and forms a part of the medial wall of the orbit. The crest, with a part of the orbital surface immediately posterior to it gives origin to the lacrimal part of the orbicularis oculi muscle. The crest ends below in a small hook, termed the lacrimal hamulus, which articulates with the maxilla and completes the upper orifice of the bony canal for the nasolacrimal duct ; the lacrimal hamulus sometimes exists as a separate piece, and is then called the lesser lacrimal bone. On the medial or nasal surface a vertical furrow corresponds 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 the furrow articulates with the ethmoid bone and completes some of the anterior ethmoidal sinuses. The anterior border of the lacrimal bone articulates with the frontal process of the maxilla: the posterior border with the orbital plate (lamina papyracea) of the ethmoid ; the superior border with the frontal bone. The posterior part of the inferior border articulates with the orbital surface of the maxilla.
Ossification.---The lacrimal bone is ossified from one centre, which appears about the twelfth week of fetal life in the membrane covering the cartilaginous nasal capsule.
Figure 374
Figure 375
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Vertebral Column