<prompt> The distance between tympanic membrane and medial wall of middle ear at centre is:3 mm4 mm6 mm2 mm  <response>: Middle ear cavity is shaped like a cube, compressed from side to side. In coronal section it resembles a biconcave disc. The veical and anteroposterior diameters are 15 mm each, and transverse diameters are: 6 mm at roof, 2 mm in the centre. 4 mm at floor 