Topographical anatomy of the guinea pig temporal bone.

Systematic anatomical description of the various structures of the temporal bone have been performed based on dissection of 16 guinea pigs (32 temporal bones). It has been found that besides two main air spaces in the middle ear, the tympanic bulla and dorsal bulla described in literature, there are also additional air cells in the mastoid process and facial nerve region in the temporal bone of a guinea pig. Moreover recesses were found in the walls of the tympanic bulla that formed almost completely separated partitions of tympanic cavity. The malleus head, the body of the incus and the superior and lateral semicircular canals as well as the facial nerve are easily accessible from the dorsal bulla. From the ventral tympanic bulla, one can access both windows and the cochlea. The semicircular canals are relatively large, the lateral canal is largest and the posterior the smallest. The cochlea has thin bony wall, and is composed of 3.5-3.75 turns.