The lacrimal bones (French: os lacrymal) are extremely thin and delicate, quadrilateral in shape, and situated at the anterior part of the inner wall of the orbit. They are the smallest of the facial bones.
The outer or orbital surface is divided by a vertical ridge into two unequal portions. The anterior smaller portion is deeply grooved to form the lacrimal sulcus, which lodges the lacrimal sac and forms the commencement of the lacrimal duct. The portion behind the ridge is smooth, and forms part of the inner wall of the orbit. The ridge gives origin to the tensor tarsi muscle, and terminates inferiorly in a hook-like process, the hamulus, which curves forward to articulate with the lacrimal tubercle of the maxilla and completes the superior orifice of the lacrimal canal. The inner surface is in relation with the two anterior cells of the ethmoid (lacrimo-ethmoid), and forms part of the infundibulum. The superior border is short, and articulates with the internal angular process of the frontal. The lower border posterior to the crest joins the inner edge of the orbital plate of the maxilla. The narrow piece, anterior to the ridge, is prolonged downwards to join the lacrimal spine of the inferior turbinal, and is called the turbinal process. The anterior border comes into relation with the posterior border of the nasal process of the maxilla. The posterior border articulates with the os planum of the ethmoid. . Articulations. - The lacrimal articulates with the ethmoid, maxilla, frontal and inferior turbinal bones.
Its arteries are derived from the infraorbital, the nasal branch of the ophthalmic, and the anterior ethmoidal.
This bone arises in the membrane overlying the cartilage of the fronto-nasal plate. Its mode of ossification is very variable. As a rule it is described as coming from one nucleus. Not infrequently the hamulus is a separate element. Sometimes the bone is divided horizontally, and a process of the os planum projects between the two halves to join the nasal process of the maxilla. More rarely the bone is represented by a group of detached ossicles resembling Wormian bones.
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