On its inner side is a small air chamber in the petrous portion of the temporal bone, called the cavity of the tympanum.
By this means the posterior surface of the petrous bone can be exposed as far inwards as the internal auditory meatus.
From the surrounding 794 mesoderm the petrous bone is formed by a process of chondrification and ossification.
The bones related to the organ of hearing, the tympanis and petrous bones, are very solid and dense in structure.
The bony labyrinth presents a series of cavities which are channelled through the substance of the petrous bone.
1540s, from Middle French petreux, from Latin petrosus "stony," from petra "rock," from Greek petra "rock, cliff, ledge, shelf of rock, rocky ridge," of uncertain origin. Possibly from PIE root *per- "to lead, pass over," if the original meaning is "bedrock" and the notion is "what one comes through to" [Watkins].
petrous pet·rous (pět'rəs)
Of stony hardness.
Of or relating to the dense hard portion of the temporal bone that forms a protective case for the inner ear.