During development, the pas of ear develops at different intervals. All of the following are of adult size at bih, EXCEPT:

Maxillary antrum reaches adult size by 15 yrs of age. At bih all three ossicles are of adult size and shape. Malleus and incus grow to adult size by 15 weeks and stapes by 18 weeks. The middle ear cavity is approximately adult sized at bih, as are the oval window, round window. Ref: Pediatric Otolaryngology, Volume 1, By Cuneyt M. Alper, Ellis M. Arjmand, Sylvan E. Stool, Margaretha L. Casselbrant, 2003, Page 134.