The development of the ethmoidal cells begins during fetal life.

It is the thinnest wall of the orbit, evidenced by pneumatized ethmoidal cells.

In some cases the air cell opens on this surface of the bone and then communicates with the posterior ethmoidal cells.

The plate covers in the middle and posterior ethmoidal cells and forms a large part of the medial wall of the orbit.

The anterior ethmoidal cells of the ethmoidal sinus open into the front part of the infundibulum as well.

More rarely it opens on both surfaces, and then communicates with the posterior ethmoidal cells and the sphenoidal sinus.

It exits into the nasal cavity to supply posterior ethmoidal cells and nasal septum; here it anastomoses with the sphenopalatine artery.

It lies between the superior nasal conchæ and middle nasal conchæ; the sphenopalatine foramen opens into it behind, and the posterior ethmoidal cells in front.

The area in front of this furrow forms part of the middle meatus of the nose; that behind it articulates with the ethmoid, and completes some of the anterior ethmoidal cells.

The bulla ethmoidalis is caused by the bulging of the middle ethmoidal cells which open on or immediately above it, and the size of the bulla varies with that of its contained cells.

Once branching from the ophthalmic artery, it accompanies the nasociliary nerve through the anterior ethmoidal canal to supply the anterior and middle ethmoidal cells, frontal sinus, and anterosuperior aspect of the lateral nasal wall.

The ethmoidal nerves, which arise from the nasociliary nerve, supply the ethmoidal cells; the posterior branch leaves the orbital cavity through the posterior ethmoidal foramen and gives some filaments to the sphenoidal sinus.

The back part of the surface is subdivided by a narrow oblique fissure, the superior meatus of the nose, bounded above by a thin, curved plate, the superior nasal concha; the posterior ethmoidal cells open into this meatus.

On it is a curved fissure, the hiatus semilunaris, limited below by the edge of the uncinate process of the ethmoid and above by an elevation named the bulla ethmoidalis; the middle ethmoidal cells are contained within this bulla and open on or near to it.

The middle ethmoidal cells open into the central part of this meatus, and a sinuous passage, termed the infundibulum, extends upward and forward through the labyrinth and communicates with the anterior ethmoidal cells, and in about 50 per cent.

The lateral margin of the anterior surface is serrated, and articulates with the lamina papyracea of the ethmoid, completing the posterior ethmoidal cells; the lower margin articulates with the orbital process of the palatine bone, and the upper with the orbital plate of the frontal bone.