8. THE ORGAN OF HEARING

The External Ear

The external ear consists of the auricle and the external auditory meatus.

The auricle, commonly called the ear, is formed of elastic cartilage covered with skin. The external auditory meatus consists of two parts: cartilaginous and bony. The cartilaginous auditory meatus is a continuation of the auricular cartilage in the form of a groove open upward and to the back. Its internal end is joined by means of connective tissue with the edge of the tympanic part of the temporal bone.

The Tympanic Membrane

The tympanic membrane or ear drum is located at the junctions of the external and middle ears. The membrane is inclined because of the oblique position of the medial end of the auditory meatus, but in newborns it is almost horizontal. The substance of the membrane itself between the two layers consists of fibrous connective tissue, the fibers of which in the peripheral part of the membrane run in a radial direction and in the central part in a circular direction. In the upper part the tympanic membrane contains no fibrous fibers and consists only of the skin and mucous layers and a thin stratum of loose tissue between them.

The Middle Ear

The middle ear consists of the tympanic cavity and the auditory tube through which it communicates with the nasopharynx. The tympanic cavity is situated in the base of the pyramid of the temporal bone between the external auditory meatus and the labyrinth (internal ear). It contains a chain of three small ossicles transmitting sound vibrations from the tympanic membrane to the labyrinth.

The Internal Ear

The internal ear, or the labyrinth, is located in the depth of the pyramid of the temporal bone between the tympanic cavity and the internal auditory meatus, through which the auditory nerve emerges from the labyrinth.