Orbit (anatomy)

In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents. In the adult human, the volume of the orbit is 30 mL, of which the eye occupies 6.5 mL. The orbital contents comprise the eye, the orbital and retrobulbar fascia, extraocular muscles, cranial nerves II, III, IV, V, and VI, blood vessels, fat, the lacrimal gland with its sac and nasolacrimal duct, the eyelids, medial and lateral palpebral ligaments, check ligaments, the suspensory ligament, septum, ciliary ganglion and short ciliary nerves.

Foramina and fissures

The orbits are conical or four-sided pyramidal cavities, which open into the midline of the face and point back into the head. Each consists of a base, an apex and four walls. There are two important foramina, or windows, two important fissures, or grooves, and one canal surrounding the globe in the orbit. There is a supraorbital foramen, an infraorbital foramen, a superior orbital fissure, an inferior orbital fissure and the optic canal, each of which contains structures that are crucial to normal eye functioning. The supraorbital foramen contains the supraorbital nerve, the first division of the trigeminal nerve or V1 and lies just lateral to the frontal sinus. The infraorbital foramen contains the second division of the trigeminal nerve, the infraorbital nerve or V2, and sits on the anterior wall of the maxillary sinus. Both foramina are crucial as potential pathways for cancer and infections of the orbit to spread into the brain or other deep facial structures.