Microsurgical Anatomy of the Orbit: The Rule of Seven

Figure 2

kull bones are added to gradually rebuild the bony orbit, starting along the medial orbital wall. (a) The ethmoid. The quadrangular orbital plate of the ethmoid constitutes the center of the medial orbital wall and separates the orbit from the medially located nasal cavity. (b) The frontal bone. The orbital plate of the ethmoid articulates superiorly with the medial edge of the orbital plate of the frontal bone. The anterior and posterior ethmoidal notches that exist in both of these plates, when combined, form the anterior and posterior ethmoidal canals. (c) Parasagittal cut through the right orbit, showing the combination of the orbital plates of the frontal (blue) and ethmoidal bone (brown) to form the ethmoidal canals (red). (d) Maxillae. Inferiorly, the ethmoid articulates with the orbital surface of the maxilla. (e) Ethmoid, frontal bone, and maxilla are combined. (f) Lacrimal bone. The upper part of the lacrimal bone is a thin plate of bone located between the anterior edge of the ethmoid and the frontal process of the maxilla. (g) In the articulated skull, the lacrimal bone can be recognized as a curved plate of bone, which forms the anteromedial 2/3 of cranial opening of the nasolacrimal duct. (h) Posteriorly, the ethmoid articulates with the body of the sphenoid, therefore completing the medial wall of the orbit. (i) The sphenoid contributes to the bony formation of the orbit through its body, lesser and greater wings. (j) The greater sphenoid wings, laterally directed, join the orbital surface of the zygomatic bone to form the lateral orbital wall. (k) The zygomatic bone. Lateral surface. (l) The zygomatic bone. Orbital surface. (m) The lateral wall of the orbit is formed by the combination of the orbital surfaces of the greater sphenoid wing (green) and the zygomatic bone (pink). (n) An axial cut has been made through the right orbit, removing its roof. The greater wing of the sphenoid (green) is, on the endocranial side, the anterior limit of the middle fossa. The zygomatic bone (pink), in contrast, forms the anterior limit of the temporal fossa, where the temporal muscle is located. (o) The sphenoid (green), maxillae (yellow) and zygomatic bones (pink) have been combined. (p) The anterior lip of the inferior orbital fissure is formed by the orbital surface of the maxilla and the orbital process of the palatine bone (red). (q) The palatine bones have a horizontal part, which form the posterior part of the hard palate, and a vertical part (perpendicular plate). (r)-(s). The palatine bones face posteriorly the pterygoid processes of the sphenoid bone, across the pterygomaxillary fissures while the orbital process (red) abuts along the floor of the orbit, between the maxilla and the ethmoid. (t) The inferior orbital fissure is located along the lateral wall and the floor of the orbit. (u) The inferior orbital fissure is an important surgical landmark in the orbit. The lateral part of the fissure is filled with smooth muscle and fat tissue, making it a suitable point to bear the bony cuts needed to remove part of the roof and lateral walls with corresponding orbital rim, as in the cranio-orbito-zygomatic approaches (Insert).