The bulla is a swelling formed on the lateral wall of the middle meatus. This bulge is produced by the middle ethmoidal air cells. These air sinuses communicate with the meatus just superiorly to the bulla.

The term ethmoid comes from the Greek term ethmos meaning sieve. Galen called the bone the sieve-like bone because of the many small foramina that transmit the olfactory nerves to the nasal cavity. Bulla arises from the Latin and means a blister or bubble.