Structure and Development of Ethmoid Sinus
- Ethmoid air cells are thin-walled cavities in the ethmoidal labyrinth, representing invaginations of the nasal mucous membrane into the ethmoid bone.
- They are situated between the superior parts of the nasal cavities and the orbits, separated by thin bony lamellae.
- At birth, 3-4 air cells are present, increasing to 5-15 by adulthood.
- There are 5-15 air cells in each ethmoid bone in adults, with a combined volume of 2-3mL.

Drainage of Ethmoid Sinus
- Anterior ethmoidal cells drain into the middle nasal meatus through the ethmoidal infundibulum.
- Middle ethmoidal cells drain directly into the middle nasal meatus.
- Posterior ethmoidal cells drain directly into the superior nasal meatus at the sphenoethmoidal recess.
- Sometimes, one or more posterior ethmoidal cells open into the sphenoidal sinus.

Lamellae of Ethmoid Sinus
- The ethmoidal labyrinth is divided by multiple obliquely oriented, parallel lamellae.
- The first lamella is equivalent to the uncinate process of the ethmoid bone.
- The second lamella corresponds to the ethmoid bulla.
- The third lamella is the basal lamella, separating anterior and posterior ethmoid cells.
- The fourth lamella is equivalent to the superior nasal concha.

Innervation of Ethmoid Sinus
- Ethmoidal air cells receive sensory innervation from the anterior and posterior ethmoidal nerves, derived from the ophthalmic branch of the trigeminal nerve.
- Orbital branches of the pterygopalatine ganglion carry postganglionic parasympathetic nerve fibers for mucous secretion from the facial nerve.

Additional Information
- Ethmoidal cells and maxillary sinuses are present at birth.
- Sometimes, one or more posterior ethmoidal cells open into the sphenoidal sinus.

Ethmoid sinus (Wikipedia)

The ethmoid sinuses or ethmoid air cells of the ethmoid bone are one of the four paired paranasal sinuses. Unlike the other three pairs of paranasal sinuses which consist of one or two large cavities, the ethmoidal sinuses entail a number of small air-filled cavities ("air cells"). The cells are located within the lateral mass (labyrinth) of each ethmoid bone and are variable in both size and number. The cells are grouped into anterior, middle, and posterior groups; the groups differ in their drainage modalities, though all ultimately drain into either the superior or the middle nasal meatus of the lateral wall of the nasal cavity.

Ethmoid sinus
Frontal view of paranasal sinuses
Coronal section of nasal cavities.
Details
Nerve	posterior ethmoidal nerve
Identifiers
Latin	Cellulae ethmoidales, labyrinthi ethmoidales
MeSH	D005005
TA98	A06.1.03.005
TA2	3180
FMA	84115
Anatomical terms of bone [edit on Wikidata]