- first to develop.
- rudimentary at birth.
- 2mm/year growth rate in vertical dimension
- growth till end of puberty
- 1 year: lateral margin of sinus projects under medial orbital wall.
- 4 years: extends laterally past infraorbital canal.
- 9 years: reaches maxillary bone and plane of hard palate
- at birth: developed anteriorly more than posteriorly.
- lack of pneumatization of posterior ethmoids – normal till 6 years.
- eventually posterior ethmoid air cells larger and fewer than anterior.
- last to develop – agger nasi, Haller and concha bullosa.
- soon after birth, begin to pneumatize; as early as 2 years.
- pneumatization proceeds inferiorly, posteriorly and laterally.
- first presphenoid, followed by basisphenoid, greater wings and pterygoid processes.
- last to develop.
- extensions of anterior ethmoid air cells.
- earliest at 2 years in the orbital processes of frontal bone
- 4 years: nasion
- 8 years: orbital roof.
- 10 years: vertical portion of frontal bone.
- growth till end of puberty.