The Accessory Sinuses of the nose are important on account of their frequent involvement in nasal affections. The sinuses to be considered consist of two groups-a posterior, opening above the middle turbinate, and consisting of the sphenoidal and posterior ethmoidal ; and an anterior, opening below the middle turbinate, and consisting of anterior ethmoidal, frontal, and superior maxillary. With the exception of the ethmoidal cells, which, unlike the others, are not formed by absorption of diploic cancellous bone, these sinuses are either non-existent or rudimentary at birth-the antrum of Highmore, for example, consisting of a slit-like indentation.