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The membranous bag itself contains a similar fluid, the endolymph. In this fluid are found some minute crystals of lime like tiny particles of sand, called otoliths, or ear-stones. Every movement of the fluid itself throws these grains from side to side. Bony internal Ear of Right Side.
The outer portion is surrounded by a membrane which serves as periosteum to the bone and, at the same time, holds the liquid belonging to this part, called the perilymph. The inner portion, called the membranous labyrinth, consists essentially of a closed membranous sac, which is filled with the endolymph. The auditory nerve terminates in this portion of the internal ear. Vestibule. 2. Cochlea. 3.
Its greatest length is not more than three fourths of an inch and its greatest diameter not more than one half of an inch. It is filled with a liquid which at one place is called the perilymph, and at another place the endolymph. It is a double organ, being made up of an outer portion which lies next to the bone, and which surrounds an inner portion of the same general form.
*The Scala Media.*—This division of the cochlea lies parallel to and between the other two divisions. It is above the scala tympani and below the scala vestibula, and is separated from each by a membrane. The scala media belongs to the membranous portion of the internal ear and is, therefore, filled with the endolymph.
The endolymph and the tiny grains of ear-sand now perform their part in this marvelous and complex mechanism. They are driven against the sides of the membranous bag, and so strike the ends of the nerves of hearing, which transmit the auditory impulses to the seat of sensation in the brain.
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