Skull: Anterior View

The convex anterior surface of the frontal bone is relatively smooth, but there are frontal tuberosities, or elevations, on each side. In early life, a median suture separates the two halves of the developing bone. This suture normally fuses between ages 6 and 10 years but occasionally persists as the metopic suture. The two orbital openings are roughly quadrangular and have supraorbital, infraorbital, medial, and lateral borders. The supraorbital notch, or fissure, carries the corresponding nerve and vessels. The infraorbital foramen, located about 1 cm below the infraorbital margin, transmits the nerve and vessels of the same name. The orbits are somewhat pyramidal in shape, with the quadrangular openings, or bases, directed forward and slightly outward, whereas the apexes correspond to the medial ends of the superior orbital fissures.

The superior wall (roof) separates the orbital contents from the brain and meninges in the anterior cranial fossa. Anteromedially, it is hollowed out by a variably sized frontal sinus, and anterolaterally, there is a shallow lacrimal fossa for the orbital part of the lacrimal gland. Posteriorly, the optic canal (foramen) lies between the two roots of the lesser wing of the sphenoid bone, just above the medial end of the superior orbital fissure; it transmits the optic (II) nerve and ophthalmic artery.

The inferior wall (floor) is formed mainly by the orbital surface of the maxilla, which separates the orbit from the maxillary sinus (antrum). A groove for the infraorbital nerve and vessels ends in the infraorbital foramen.

The thin medial wall separates the orbit from the ethmoidal air cells, the anterior part of the sphenoidal sinus, and the nasal cavity. At its anterior end, the lacrimal fossa is continuous below with the short nasolacrimal canal that opens into the inferior nasal meatus. The thicker lateral wall separates the orbit from the temporal fossa anteriorly and from the middle cranial fossa posteriorly. The orbital surface of the zygomatic bone shows a foramen for the zygomatic nerve, which bifurcates within the bone to emerge on the cheek and temporal fossa as the zygomaticofacial and zygomaticotemporal nerves, respectively.

The lateral wall and roof are continuous anteriorly but diverge posteriorly to bound the superior orbital fissure, which lies between the greater and lesser wings of the sphenoid bone and opens into the middle cranial fossa. The fissure transmits the oculomotor (III) and trochlear (IV) nerves, the lacrimal, frontal and nasociliary branches of the ophthalmic nerve, the abducens (VI) nerve, the ophthalmic veins, and small meningeal vessels.

The lateral wall and floor of the orbit are also continuous anteriorly but are separated posteriorly by the inferior orbital fissure, most of which is located between the greater wing of the sphenoid bone and the orbital surface of the maxilla. The inferior orbital fissure connects the orbit with the pterygopalatine and infratemporal fossae. The maxillary nerve passes from the pterygopalatine fossa into the orbit through the inferior orbital fissure and continues forward as the infraorbital nerve. Anastomotic channels between the orbital and pterygoid venous plexuses, and orbital fascicles from the pterygopalatine ganglion, also traverse this fissure.

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