Orbital part of frontal bone

Surfaces

• The inferior surface of each orbital plate is smooth and concave, and presents, laterally, under cover of the zygomatic process, a shallow depression, the lacrimal fossa, for the lacrimal gland; near the nasal part is a depression, the fovea trochlearis, or occasionally a small trochlear spine, for the attachment of the cartilaginous pulley of the obliquus oculi superior.
• The superior surface is convex, and marked by depressions for the convolutions of the frontal lobes of the brain, and faint grooves for the meningeal branches of the ethmoidal vessels.
• * The ethmoidal notch separates the two orbital plates; it is quadrilateral, and filled, in the articulated skull, by the cribriform plate of the ethmoid.
• ** The margins of the notch present several half-cells which, when united with corresponding half-cells on the upper surface of the ethmoid, complete the ethmoidal air cells.
• * Two grooves cross these edges transversely; they are converted into the anterior and posterior ethmoidal canals by the ethmoid, and open on the medial wall of the orbit.
• ** The anterior canal transmits the nasociliary nerve and anterior ethmoidal vessels,
• ** the posterior, the posterior ethmoidal nerve and vessels.
• In front of the ethmoidal notch, on either side of the frontal spine, are the openings of the frontal air sinuses.
• * These are two irregular cavities, which extend backward, upward, and lateralward for a variable distance between the two tables of the skull; they are separated from one another by a thin bony septum, which often deviates to one or other side, with the result that the sinuses are rarely symmetrical.
• * Absent at birth, they are usually fairly well-developed between the seventh and eighth years, but only reach their full size after puberty.
• * They vary in size in different persons, and are larger in men than in women.
• * They are lined by mucous membrane, and each communicates with the corresponding nasal cavity by means of a passage called the frontonasal duct.

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