Boundaries and margins of the orbit
The base of the orbital pyramid forms the orbital opening (Aditus orbitalis). It is clearly defined by four margins that are easily palpable on the face:
- Supraorbital margin (Margo supraorbitalis);
- Infraorbital margin (Margo infraorbitalis);
- Lateral margin (Margo lateralis);
- Medial margin (Margo medialis).
The apex of the pyramid is directed backward and medially, transitioning into the optic canal (Canalis opticus). Through this canal, the orbital cavity directly communicates with the middle cranial fossa.
Structure of the walls
The orbital cavity is bounded by four walls, each formed by different bony structures:
- Superior wall (Paries superior). Formed by the orbital part of the frontal bone (Pars orbitalis) and the lesser wings of the sphenoid bone.
- Inferior wall (Paries inferior). Formed by the orbital surfaces of two bones: the body of the maxilla and the zygomatic bone.
- Lateral wall (Paries lateralis). The most massive wall. Formed by the zygomatic process of the frontal bone, the orbital surface of the greater wing of the sphenoid bone, and the orbital surface of the zygomatic bone.
- Medial wall (Paries medialis). Formed by the frontal process of the maxilla, the lacrimal bone, the orbital plate of the ethmoid bone, and the lateral surface of the body of the sphenoid bone. This wall also features the fossa for the lacrimal sac (Fossa sacci lacrimalis), which continues into the lacrimal groove (Sulcus lacrimalis) and further into the nasolacrimal canal (Canalis nasolacrimalis).
Key communications, fissures, and their contents
The orbit is rich in foramina and fissures through which vital neurovascular bundles pass. Let's examine the main pathways of communication.
Connection with the cranial cavity:
- Optic canal (Canalis opticus): transmits the optic nerve (N. opticus, CN II) and the ophthalmic artery (A. ophthalmica), which gives rise to the central retinal artery.
- Superior orbital fissure (Fissura orbitalis superior): transmits the oculomotor (N. oculomotorius, CN III), trochlear (N. trochlearis, CN IV), abducens (N. abducens, CN VI) nerves, and the ophthalmic nerve (N. ophthalmicus, first branch of CN V). Vascular structures include the superior ophthalmic vein (V. ophthalmica superior) and sometimes the anterior meningeal branches of the ophthalmic artery.
Connection with the face and other areas:
- Inferior orbital fissure (Fissura orbitalis inferior): contains the infraorbital (N. infraorbitalis) and zygomatic (N. zygomaticus) nerves, infraorbital vessels, and connects the orbit with the inferior ophthalmic vein.
- Infraorbital canal (Canalis infraorbitalis): leads to the face, the maxillary sinus, and the dental alveoli. Contains the corresponding nerve, artery, and veins. It opens via the infraorbital foramen (Foramen infraorbitale), where the nerve branches into the lesser goose's foot (Pes anserinus minor).
- Supraorbital and frontal notches/foramina: connect the superior wall with the face. The supraorbital notch transmits the frontal nerve and supraorbital vessels, while the frontal notch transmits the supratrochlear vessels and nerve (N., A., V. supratrochleares).
- Zygomaticoorbital foramen (Foramen zygomaticoorbitale): located on the lateral wall, transmits the zygomatic nerve, which then divides and emerges onto the face and into the temporal fossa through the zygomaticofacial and zygomaticotemporal foramina.
- Ethmoidal foramina (anterior and posterior): located on the medial wall, connecting the orbit with the ethmoidal air cells, nasal cavity, and anterior cranial fossa. They transmit the corresponding arteries, veins, and nerves.
Class and exam questions
Which bones form the medial wall of the orbit?
It includes the frontal process of the maxilla, the lacrimal bone, the orbital plate of the ethmoid bone, and the lateral surface of the body of the sphenoid bone.
Through which foramen does the orbit communicate with the middle cranial fossa?
Primarily via the optic canal (Canalis opticus), which forms the apex of the orbital pyramid.
What passes through the superior orbital fissure?
It transmits cranial nerves III, IV, and VI, the ophthalmic nerve (a branch of CN V), and the superior ophthalmic vein into the orbit.
Where is the lesser goose's foot (Pes anserinus minor) formed?
It is formed by the branches of the infraorbital nerve after it emerges onto the face through the infraorbital foramen.
What else to study on this topic
- Detailed topography of vessels and nerves of the superior orbital fissure
- Branching of the infraorbital nerve (formation of the lesser goose's foot)
- Innervation and blood supply of the teeth via alveolar canals
- Structure and course of the nasolacrimal canal
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