Tegmen tympani
A thin plate of bone that covers the middle ear and separates it from the cranial cavity.
The medial part of the tegmen tympani develops form the otic capsule during chondral ossification, and the lateral portion of the tegmen tympani develops by way of membranous ossification 1).
1)
Tóth M, Helling K, Baksa G, Mann W. Localization of congenital tegmen tympani defects. Otol Neurotol. 2007;28:1120–1123.