Human Anatomy, Part 1 - K. A. Dyubenko, A. K. Kolomiytsev, Yu. B. Chaykovsky 2002

Special Part
Axial skeleton, sceleton axiale — The skull as a whole
Orbit

The eye socket, or orbit (orbita), is a paired four-sided cavity, cavitas orbitalis (LNA), resembling a pyramid, which houses the visual apparatus (Fig. 52). It features an orbital opening, aditus orbitalis, bounded by the orbital margin, margo orbitalis. The depth of the orbit in an adult ranges from 4 to 5 cm, with a width of about 4 cm. This is crucial to consider in clinical practice when probing orbital wounds, inserting injection needles, etc. The orbit is bounded by four walls: superior, inferior, medial, and lateral, lined with periosteum, periorbita.

The superior wall, paries superior, is formed by the orbital surface of the Frontal bone and the lesser wing of the Sphenoid bone. It separates the orbit from the anterior cranial fossa and the Brain.

The inferior wall, paries inferior, is formed by the orbital surface of the Maxilla, the Zygomatic bone, and the orbital process of the Palatine bone. The inferior wall serves as the roof of the maxillary sinus (antrum of Highmore), which must be taken into account in clinical practice.

The medial wall, paries medialis (Fig. 53), is formed by the frontal process of the maxilla, the Lacrimal bone, the orbital plate of the Ethmoid bone, the body of the sphenoid bone, and partially the orbital surface of the frontal bone. The medial wall is thin and features several openings for the passage of Blood Vessels and nerves. This anatomical feature readily explains the spread of pathological processes from the ethmoid air Cells into the orbit and vice versa.

The lateral wall, paries lateralis, is formed by the orbital surface of the zygomatic bone, the greater wing of the sphenoid bone, and the orbital part of the frontal bone. It separates the orbit from the temporal fossa.

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Fig. 52. The eye socket [orbit], orbita (after F. Kiss and J. Szentágothai)

Within the orbit, there are several openings and fissures that connect it to other cranial structures: the optic canal, canalis opticus; the inferior orbital fissure, fissura orbitalis inferior; the superior orbital fissure, fissura orbitalis superior; the zygomaticoorbital foramen, foramen zygomaticoorbitale; the nasolacrimal canal, canalis nasolacrimalis; and the anterior and posterior ethmoidal foramina, foramen ethmoidalis anterior et posterior.

Deep within the orbit, at the junction of the superior and lateral walls, lies a comma-shaped fissure (the superior orbital fissure, fissura orbitalis superior), formed by the body, greater wing, and lesser wing of the sphenoid bone. It connects the orbit to the cranial cavity (middle cranial fossa). Passing through the superior orbital fissure are all the motor NERVES OF THE Eyeball: the Oculomotor nerve, n. oculomotorus; the Trochlear nerve, n. trochlearis; the Abducens nerve, n. abducens; along with the ophthalmic nerve, n. ophthalmicus, and the main venous collector of the orbit (the superior ophthalmic vein, v. ophthalmica superior). The concentration of these vital structures within the superior orbital fissure explains why pathology in this region results in a distinct symptom complex known as superior orbital fissure syndrome.

Fig. 53. The orbit, orbita (medial wall of the right orbit)

At the boundary between the lateral and inferior walls of the orbit runs the inferior orbital fissure, fissura orbitalis inferior. It is bounded by the lower margin of the greater wing of the sphenoid bone and the body of the maxilla. In its anterior part, the fissure connects the orbit with the infratemporal fossa, and in its posterior part, with the pterygopalatine fossa. Passing through the inferior orbital fissure are venous anastomoses connecting the orbital Veins with the pterygopalatine venous plexus and the deep facial vein, v. facialis profunda.