E, Floor of the right orbit viewed from above. The orbital floor is formed by the orbital plate of the maxilla, the orbital surface of the zygoma, and the orbital process of the palatine bone. The orbital floor, which is very thin, forms most of the roof of the maxillary sinus. The floor is continuous with the medial wall, except in the most anterior part where the floor is perforated by the nasolacrimal canal. The anterior part of the floor is continuous with the lateral wall, but posteriorly, the floor and lateral wall are separated by the inferior orbital fissure. The infraorbital groove, which transmits the infraorbital branch of the maxillary nerve, leads forward out of the inferior orbital fissure to cross the floor to reach the infraorbital canal, which ends in the infraorbital foramen. The posterior part of the inferior orbital fissure communicates below with the pterygopalatine fossa, and the anterior part communicates with the infratemporal fossa. F, Inferior aspect of the roof of the maxillary sinus, which also forms the floor of the orbit. The greater sphenoid wing forms much of the middle fossa floor and the posterior part of the lateral orbital wall. The pterygopalatine fossa is located behind the maxillary sinus and contains the terminal part of the maxillary artery, the maxillary nerve, and the pterygopalatine ganglion and some branches of all three structures. The pterygopalatine fossa opens through the pterygomaxillary fissure into the infratemporal fossa, which is located below the greater sphenoid wing and contains the pterygoid muscles, a segment of the maxillary artery, branches of the mandibular nerve and the pterygoid venous plexus. The medial wall of the pterygopalatine fossa is formed by the perpendicular plate of the palatine bone and contains an opening, the sphenopalatine foramen, that communicates with the nasal cavity. G, Lateral view of the medial wall of the right orbit. The medial wall is formed by the frontal process of the maxilla, the lacrimal bone, the orbital plate of the ethmoid bone, and the sphenoid body. The medial wall is extremely thin in the area of the orbital plate of the ethmoid bone, which separates the orbit and ethmoidal sinuses. The lacrimal sac, which sits in the lacrimal groove, drains into the nasal cavity through the nasolacrimal canal. The lacrimal groove is formed by the frontal process of the maxilla anteriorly and the lacrimal bone posteriorly. The anterior and posterior ethmoidal foramina, which transmit the anterior and posterior ethmoidal branches of the ophthalmic artery and the anterior and posterior ethmoidal branches of the nasociliary nerve, pass through the frontoethmoidal suture or the adjacent part of the frontal bone and open into the anterior cranial fossa along the lateral edge of the cribriform plate. The pterygomaxillary fissure opens into the pterygopalatine fossa. H, Lateral aspect of the lateral wall of the right orbit. The zygoma forms the lateral rim and the anterior part of the lateral wall of the orbit. Behind the zygoma, the lateral wall of the orbit is formed by the greater sphenoid wing. The temporal fossa is located between the zygomatic arch and the greater wing. The temporalis muscle arises in the temporal fossa and extends downward medial to the zygomatic arch to attach to the coronoid process of the mandible. The infratemporal fossa is located medial to the temporal fossa, below the greater sphenoid wing. The pterygomaxillary fissure, located between the posterior maxilla and the pterygoid process, opens into the pterygopalatine fossa. (Images courtesy of AL Rhoton, Jr.)