|Henry Gray (18251861). Anatomy of the Human Body. 1918.|
|and the stylomastoid branch of the posterior auricular, which supplies the back part of the tympanic cavity and mastoid cells. The smaller arteries arethe petrosal branch of the middle meningeal, which enters through the hiatus of the facial canal; a branch from the ascending pharyngeal, and another from the artery of the pterygoid canal, which accompany the auditory tube; and the tympanic branch from the internal carotid, given off in the carotid canal and perforating the thin anterior wall of the tympanic cavity. The veins terminate in the pterygoid plexus and the superior petrosal sinus. The nerves constitute the tympanic plexus, which ramifies upon the surface of the promontory. The plexus is formed by (1) the tympanic branch of the glossopharyngeal; (2) the caroticotympanic nerves; (3) the smaller superficial petrosal nerve; and (4) a branch which joins the greater superficial petrosal.|
| The tympanic branch of the glossopharyngeal (Jacobsons nerve) enters the tympanic cavity by an aperture in its floor close to the labyrinthic wall, and divides into branches which ramify on the promontory and enter into the formation of the tympanic plexus. The superior and inferior caroticotympanic nerves from the carotid plexus of the sympathetic pass through the wall of the carotid canal, and join the branches of the tympanic branch of the glossopharyngeal. The branch to the greater superficial petrosal passes through an opening on the labyrinthic wall, in front of the fenestra vestibuli. The smaller superficial petrosal nerve, from the otic ganglion, passes backward through a foramen in the middle fossa of the base of the skull (sometimes through the foramen ovale), and enters the anterior surface of the petrous part of the temporal bone through a small aperture, situated lateral to the hiatus of the facial canal; it courses downward through the bone, past the genicular ganglion of the facial nerve, receiving a connecting filament from it, and enters the tympanic cavity, where it communicates with the tympanic branch of the glossopharyngeal, and assists in forming the tympanic plexus.|
| The branches of distribution of the tympanic plexus are supplied to the mucous membrane of the tympanic cavity; a branch passes to the fenestra vestibuli, another to the fenestra cochleæ, and a third to the auditory tube. The smaller superficial petrosal may be looked upon as the continuation of the tympanic branch of the glossopharyngeal through the plexus to the otic ganglion.|
| In addition to the tympanic plexus there are the nerves supplying the muscles. The Tensor tympani is supplied by a branch from the mandibular through the otic ganglion, and the Stapedius by a branch from the facial.|
| The chorda tympani nerve crosses the tympanic cavity. It is given off from the sensory part of the facial, about 6 mm. before the nerve emerges from the stylomastoid foramen. It runs from below upward and forward in a canal, and enters the tympanic cavity through the iter chordæ posterius, and becomes invested with mucous membrane. It traverses the tympanic cavity, crossing medial to the tympanic membrane and over the upper part of the manubrium of the malleus to the carotid wall, where it emerges through the iter chordæ anterius (canal of Huguier).|
|1d. 4. The Internal Ear or Labyrinth|
The internal ear is the essential part of the organ of hearing, receiving the ultimate distribution of the auditory nerve. It is called the labyrinth, from the complexity of its shape, and consists of two parts: the osseous labyrinth, a series of cavities within the petrous part of the temporal bone, and the membranous labyrinth, a series of communicating membranous sacs and ducts, contained within the bony cavities.
The Osseous Labyrinth (labyrinthus osseus) (Figs. 920, 921).The osseous labyrinth consists of three parts: the vestibule, semicircular canals, and cochlea. These are cavities hollowed out of the substance of the bone, and lined by periosteum; they contain a clear fluid, the perilymph, in which the membranous labyrinth is situated.
The Vestibule (vestibulum).The vestibule is the central part of the osseous labyrinth, and is situated medial to the tympanic cavity, behind the cochlea, and in front of the semicircular canals. It is somewhat ovoid in shape, but flattened transversely; it measures about 5 mm. from before backward, the same from above downward, and about 3 mm. across. In its lateral or tympanic wall is the fenestra vestibuli, closed, in the fresh state, by the base of the stapes and annular ligament. On its medial wall, at the forepart, is a small circular depression, the recessus sphæricus, which is perforated, at its anterior and inferior part, by several minute holes (macula cribrosa media) for the passage of filaments of the acoustic nerve to the saccule; and behind this depression is an oblique ridge, the crista vestibuli,