tympanic antrum

It is called the tympanic antrum, and must be distinguished from the mastoid cells, though it communicates with them.

The mastoid or posterior wall is wider above than below, and presents for examination the entrance to the tympanic antrum, the pyramidal eminence, and the fossa incudis.

The stylomastoid artery enters the stylomastoid foramen and supplies the tympanic cavity, the tympanic antrum and mastoid cells, and the semicircular canals.

Between the posterior wall of the external acoustic meatus and the posterior root of the zygomatic process is the area called the suprameatal triangle (Macewen), or mastoid fossa, through which an instrument may be pushed into the tympanic antrum.

The tympanic antrum is a cavity of some considerable size at the time of birth; the mastoid air cells may be regarded as diverticula from the antrum, and begin to appear at or before birth; by the fifth year they are well-marked, but their development is not completed until toward puberty.

It is situated on the anterior (frontal) surface of the petrous portion of the temporal bone close to its angle of junction with the squama temporalis; it is prolonged backward so as to roof in the tympanic antrum, and forward to cover in the semicanal for the tensor tympani muscle.