Fig. 11 INTERNAL EAR AND ITS TOPOGRAPHICAL RELATIONSHIPS TO THE STRUCTURES AT THE BASE OF THE CRANIUM
The labyrinth in all parts is exposed. The snail-shaped cochlea (86) is cut open through its basal coil where it is widest. Two of the three semicircular canals, the superior and the lateral, and the vestibular recesses for the utricle and the saccule of the vestibule (85) are uncovered. The entire labyrinth is embedded in the compact petrous portion of the temporal bone which contrasts with the spongy appearance of the mastoid process (9). Between the two is a section of the facial nerve (VII) enclosed in its bony channel. The tympanic cavity is reduced to a narrow semilunar space between the cochlea and the upper bulb of the internal jugular vein (12b), and is separated from the latter by a thin bony lamina. Just medial to the vein and intimately applying to the petrous pyramid winds the thick internal carotid artery (25b) as it rises on its way to the cranial cavity. Important nerves are found either in the floor of the cranial cavity (V) or emerging from the base of the skull (VII, IX, X, XI XII).