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Before studying the anatomy and function of the trigeminal nerve, it is important to understand the complex planes of section used in the illustration. They were chosen to showcase all branches of the trigeminal nerve in a single illustration and to emphasize the course of these branches through important foramina (holes) in the skull. The diagram at left includes a superior view of a coronally sectioned skull (labeled anterior and posterior) aligned with an anterior view of an intact skull. Red lines represent the planes of section described below.

The primary "parasagital" plane of section (see superior view) curves just lateral to the superior orbital fissure, foramen rotundum, and foramen ovale. This allows clear visualization of the ophthalmic nerve (V1), maxillary nerve (V2), and mandibular nerve (V3) as they enter the skull through their respective foramina. Superiorly and anteriorly, this "parasagital" plane cuts through the supraorbital foramen (see dotted line), then curves laterally to end with a coronal orientation (see anterior view).

The zygomatic bone is "shaved" by a second plane beginning with a coronal orientation just lateral to the infraorbital foramen and curving to a parasagital plane around the zygomaticofacial foramen (see anterior view). Additionally, the zygomatic bone has been transected coronally above the zygomaticofacial foramen. The result is a curved segment of bone resembling half of the letter "u" containing the zygomaticofacial foramen (see anterior view). The lacrimal gland is shown "floating" in its in situ superior lateral location even though the orbital wall has been removed in that area.

A "square" segment of superficial bone is removed from the lateral aspect of the maxilla creating a "window" (see anterior view). This allows visualization of superior alveolar branches coursing from the roots of the teeth as well as the lateral aspect of the mucous membrane of the maxillary sinus. It should be noted that this is the "back side" of the mucosa that lines the maxillary sinus; it is shown only to demonstrate how thin a segment of bone separates the maxillary sinus from the teeth (important clinically as dental infections can easily spread to the maxillary sinus).

Finally, the coronoid process of the mandible has been removed to allow visualization of the buccal nerve (not marked in red on diagram at left).