Fig. 9 VIEW OF THE DEEP STRUCTURES OF THE HEAD IN A PLANE PASSING THROUGH THE MIDDLE EAR AND EUSTACHIAN TUBE
The tympanic cavity (82) in this figure lies wide open except for a small segment of the eardrum. Of the three auditory ossicles, the third, called stapes or stirrup, is visible in the upper part of the tympanum, above a small hole which is the round window of the cochlea. The mastoid air cells (9) are in comunication with the tympanic cavity by means of a passage, antrum (83). The facial nerve (VII), accompanied by the stylo-mastoid artery (66), is in its canal between the mastoid (9) and the 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).