The size of the middle ear and the mastoid air cell.

The total volume for the middle ear and mastoid air cells was measured in 55 temporal bones with normal ear drums from a Norwegian post-mortem material. The measurements were made by an acoustic method and checked by means of fluid filling induced by vacuum pumping. As a measuring fluid X-ray contrast medium was employed so that the degree of filling could be examined by X-ray. The volume varied between approximately 2--22 cm3 with an average round 6,5 cm3.