Ans. is 'c' i.e., Internal jugular vein o The middle ear is shaped like a cube.o When seen in the coronal section, the cavity of the middle ear is biconcave,o The boundaries of the middle ear are as follows :I Roof or tegmental wallo Separates the middle ear from the middle cranial cavity,o It is formed by a thin plate of bone called tegmen tympani.II Floor or jugular wallo Formed by a thin plate of bone which separates the middle ear from the superior bulb of the internal jugular vein.o The floor also presents the tympanic canaliculus which transmits the tympanic branch of the glossopharyngeal nerve.III Anterior or carotid wallo The uppermost part bears the opening of the canal of the tensor tympanio The middle part has the opening of the auditory' tubeo The inferior part of the wall is formed by a thin plate of bone which forms the posterior wall of the carotid canal. This plate separates the middle ear from the internal carotid artery.IV: Posterior or mastoid wallo Superiorly, is the aditus through which the epitympanic recess communicates with the mastoid antrumo Below it is the fossa incudis which lodges the short process of the incuso Below it is the pyramid giving attachment to the tendon of stapediuso Vertical part of the facial canal for facial nerveV. Lateral or membranous wallo Tympanic membrane along with the tympanic ring and sulcus.VI Medial or labrynthine wallo Promontory - rounded bulge produced by the first turn of the cochleao Oval window -- it is posterosuperior to the promontory'. It is closed by the footplate of the stapes,o Horizontal part of the facial canal -- runs just above the oval windowo Round window -- posteroinferior to the promontory. It is closed by the secondary tympanic membrane,o Processus cochleariforims -- forms a pulley for the tendon of the tensor tympanio Prominence of the lateral semicircular canal -- above the facial canal