Boundaries and the Bony Nasal Septum
The bony nasal cavity has two primary boundaries—an entrance and an exit:
- Anterior boundary is represented by the piriform aperture (Apertura piriformis). This bony inlet is bounded by the nasal bone, the nasal notch (Incisura nasalis), and the anterior nasal spine (Spina nasalis anterior) belonging to the maxilla.
- Posterior boundary consists of the posterior nasal apertures, or choanae (Choanae), which lie lateral to the bony septum and lead into the pharynx.
In the midline, the cavity is divided by the bony nasal septum (Septum nasi osseum). Several structures contribute to its formation: the perpendicular plate of the ethmoid bone, the vomer (Vomer), the nasal spine of the frontal bone, and the sphenoidal crest located on the body of the sphenoid bone.
Superior and Inferior Walls
The bony nasal cavity is bounded by walls that form its roof and floor:
- Superior wall (roof). Formed by the nasal bone, the nasal part of the frontal bone, the cribriform plate of the ethmoid bone, and the body of the sphenoid bone.
Clinical note: via the cribriform foramina (Foramina cribrosa), the nasal cavity communicates with the anterior cranial fossa.
- Inferior wall (floor). Entirely corresponds to the bony hard palate.
Clinical note: via the incisive canals (Canales incisivi), the inferior wall connects the nasal cavity with the oral cavity.
Lateral Wall and Nasal Meatuses
The lateral wall features the most complex topography. It is formed by a complex of bones: the nasal bone, the frontal process of the maxilla, the lacrimal bone, the ethmoid labyrinth, the three nasal conchae (superior, middle, and inferior), the nasal surface of the maxilla, the perpendicular plate of the palate bone, and the medial plate of the pterygoid process of the sphenoid bone.
The nasal conchae divide the lateral space into specialized channels—nasal meatuses, each with specific communications:
- Superior nasal meatus (Meatus nasi superior) — communicates with the posterior ethmoidal cells and the sphenoid sinus.
- Middle nasal meatus (Meatus nasi medius) — leads to the anterior and middle ethmoidal cells, as well as the frontal and maxillary sinuses.
- Inferior nasal meatus (Meatus nasi inferior) — contains the opening of the nasolacrimal canal (Canalis nasolacrimalis).
- Common nasal meatus (Meatus nasi communis) — the narrow vertical space situated between all conchae and the nasal septum.
- Nasopharyngeal meatus (Meatus nasopharyngeus) — directed toward the nasopharynx.
Additionally, the sphenopalatine foramen (Foramen sphenopalatinum) is located on the lateral wall, through which the nasal cavity communicates with the pterygopalatine fossa.
Adjacent Structures: Temporal and Infratemporal Fossae
In addition to the nasal cavity proper, several important fossae are found in this region, directly or indirectly related to it:
Temporal fossa (Fossa temporalis) Bounded superiorly by the superior temporal line, and inferiorly by the zygomatic arch and infratemporal crest. Anteriorly, its boundaries are set by the temporal line and the temporal surface of the zygomatic bone; posteriorly and medially, by the greater wing of the sphenoid bone. It communicates with the infratemporal fossa and the orbit (via the zygomaticofacial/zygomaticotemporal foramina).
Infratemporal fossa (Fossa infratemporalis) Located inferior to the temporal fossa. Bounded superiorly by the zygomatic arch and infratemporal crest, and anteriorly by the infratemporal surface of the maxilla. The medial boundary is the lateral plate of the pterygoid process, and the lateral boundary is the ramus of the mandible. Communications of the infratemporal fossa:
- with the orbit (via the inferior orbital fissure);
- with the oral cavity (via alveolar canals);
- with the pterygopalatine fossa (via the pterygomaxillary fissure);
- with the mandible (via the mandibular canal).
Pterygopalatine Fossa
The pterygopalatine fossa (Fossa pterygopalatina) is a deep, slit-like continuation of the infratemporal fossa. It has 4 walls and serves as a crucial distribution center, featuring 6 major communications:
- With the orbit — via the inferior orbital fissure.
- With the middle cranial fossa — via the foramen rotundum.
- With the external skull base — via the pterygoid canal.
- With the oral cavity — via the greater palatine canal.
- With the nasal cavity — via the sphenopalatine foramen.
- With the infratemporal fossa — via the pterygomaxillary fissure.