Which bone contributes the GREATEST portion of the nasal cavity walls and septum?

Correct answer: C. Ethmoid

• A. The MAXILLA forms most of the FLOOR of the nasal cavity (with the palatine bone) and part of the lower lateral wall, but far less of the cavity overall than the ethmoid.
• B. The VOMER forms only the POSTERIOR–INFERIOR portion of the bony septum, articulating above with the perpendicular plate of the ethmoid.
• C. CORRECT. The ETHMOID bone contributes more to the nasal cavity than any other single bone. Its CRIBRIFORM PLATE forms the roof, its PERPENDICULAR PLATE forms the upper bony nasal septum, and its labyrinth forms most of the lateral wall including the SUPERIOR and MIDDLE CONCHAE and the ethmoid air cells. It is also the only bone that contributes to the roof, the lateral wall AND the septum.
• D. The SPHENOID forms the posterior roof and the sphenoid sinus opens into the sphenoethmoidal recess, but its nasal contribution is comparatively small.

Note: The cribriform plate is thin and perforated by the olfactory nerve filaments, which is why midface trauma can cause ANOSMIA and CSF RHINORRHOEA. Never pack the nose blindly in a suspected skull-base fracture.