All are of adult size at bih except
The paranasal sinuses are hollow, air-filled cavities that are lined by a mucous membrane. The ethmoid and maxillary sinuses are present at bih. The frontal sinus develops about the second year of life and the sphenoid about the third year. Sometimes, the frontal sinuses do not develop.
Mastoid antrum
Ear Ossicles
Tympanic cavity
Maxillary antrum
Head and neck