Table XVII

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Organ of hearing

Twelve models of the ear and its parts are reproduced on a bigger scale. In the centre of the top row we have a longitudinal section of the middle ear with the tympanic cavity and the auditory (Eustachian) tubes; on the medial wall of the tympanic cavity there are the fenestra vestibuli and fenestra cochleae and, in front of these, the promontory. Placed on the top of the promontory is the tensor tympani muscle raised on the back to show the processus cochleariformis of its canal. The tympanic branch of the glossopharyngeal nerve can be seen.

The nerve enters the tympanic cavity by its canaliculus of petrous bone (here scalpelled) and ramifies on the promontory giving the carotico-tympanic nerves for the carotid plexus and the branches for the tympanic cavity, and the auditory tube; behind the tympanic cavity the facial nerve is displayed (the facial canal having been opened) together with the origin of the chorda tympani which transverses the tympanic cavity. At the side two models of the bony labyrinth of the internal ear are shown; one is seen from its lateral side showing: in the middle, the wall of the vestibule with its fenestra; antero-inferiorly, the cochlea with the fenestra cochleae at its base, and, posteroinferiorly, the three semicircular canals.

The other model is seen from its medial face: the internal acoustic meatus can be seen and, inside it, the facial and acoustic nerves and the internal auditory artery. In the middle row, a model of the whole ear can be seen from the top showing: the auricle, the tympanic cavity (open on top to display inside it che chain of the auditory ossicles) and the bony labyrinth isolated from the petrous bone. On the latter bone there are, among several nerves, some trigeminal branches of which the lingual nerve is easily recognizable because it joins the chorda tympani.

At the side there is a model of the acoustic nerve divided into the cochlear (which here is truncated), and into the vestibular nerve going to the utricle and the ampullae of membranous semicircular canals. On the bottom row there is, first, a model of the lateral wall of the tympanic cavity to which the malleus is connected.

The latter is articulated with the incus and passed over by the chorda tympani. There follow the three isolated auditory ossicles: malleus, incus and stapes (whose base is missing because it has been previously broken). Below, a model of the bony labyrinth can be seen; on this model the cavity of the vestibule, the cavity of the semicircular canals and of the cochlea have been opened; inside the cochlea there is the osseous spiral lamina which winds around and projects from the scala tympani.

There is then a model of the open bony labyrinth, with the utricle inside the vestibule and the three membranous semicircular ducts inside the semicircular canals; the osseous spinal lamina of the cochlea has been delaminated in order to show the branches of the cochlear nerve contained inside. Superiorly there is an enlarged portion of the delaminated osseous spiral lamina with the cochlear nerve going towards the foramina nervosa of the habenula perforata of the limbus spiralis.

AdminTable XVII