The ethmoid bulla (or ethmoidal bulla) is an elevation on the lateral wall of the

middle meatus In anatomy, the term nasal meatus can refer to any of the three meatuses (passages) through the skulls nasal cavity: the superior meatus (''meatus nasi superior''), middle meatus (''meatus nasi medius''), and inferior meatus (''meatus nasi inferio ...

of the

nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for respiration alongside the mouth. Behind the nose are the olfactory mucosa and the sinuses. Behind the nasal cavity, air next passes ...

. It is produced by middle

ethmoidal cells The ethmoid sinuses or ethmoid air cells of the ethmoid bone are one of the four paired paranasal sinuses. The cells are variable in both size and number in the lateral mass of each of the ethmoid bones and cannot be palpated during an extraoral ...

. It develops during the

first trimester Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ...

of gestation, and varies significantly based on the size of air cells.

Structure

The ethmoid bulla is on the lateral wall of the

of the

. It is produced by middle

, which are contained within this bulla, and open on or near to it (often just below it). Just below the bulla is a curved fissure, the

hiatus semilunaris The semilunar hiatus or hiatus semilunaris, is a crescent-shaped groove in the lateral wall of the nasal cavity just inferior to the ethmoid bulla. It is the location of the openings of the maxillary sinuses. It is bounded inferiorly and anterior ...

. The

maxillary sinus The pyramid-shaped maxillary sinus (or antrum of Highmore) is the largest of the paranasal sinuses, and drains into the middle meatus of the nose through the osteomeatal complex.Human Anatomy, Jacobs, Elsevier, 2008, page 209-210 Structure It i ...

also opens below the bulla. It is the largest among the middle ethmoidal cells.

Development

The ethmoid bulla begins to develop between 8 weeks and 12 weeks of gestation.

Variation

The size of the bulla varies with that of its contained cells. The bulla may be a pneumatised cell or a bony prominence found in middle meatus.

References

Nose {{anatomy-stub