There is a steadily increasing body of evidence that shows that the lever arm ratio is actually variable, depending on frequency. Vibrations of the stapes footplate introduce pressure waves in the inner ear. The eardrum is merged to the malleus, which connects to the incus, which in turn connects to the stapes. Since the effective vibratory area of the eardrum is about 14 fold larger than that of the oval window, the sound pressure is concentrated, leading to a pressure gain of at least 18.1. The ossicles are classically supposed to mechanically convert the vibrations of the eardrum into amplified pressure waves in the fluid of the cochlea (or inner ear), with a lever arm factor of 1.3. While the stapes is present in all tetrapods, the malleus and incus evolved from lower and upper jaw bones present in reptiles. The ossicles directly couple sound energy from the eardrum to the oval window of the cochlea. The ossicles were given their Latin names for their distinctive shapes they are also referred to as the hammer, anvil, and stirrup, respectively. The middle ear contains three tiny bones known as the ossicles: malleus, incus, and stapes. The primary function of the middle ear is to efficiently transfer acoustic energy from compression waves in air to fluid–membrane waves within the cochlea. The auditory tube (also known as the Eustachian tube or the pharyngotympanic tube) joins the tympanic cavity with the nasal cavity ( nasopharynx), allowing pressure to equalize between the middle ear and throat. The hollow space of the middle ear is also known as the tympanic cavity and is surrounded by the tympanic part of the temporal bone. The mammalian middle ear contains three ossicles (malleus, incus, and stapes), which transfer the vibrations of the eardrum into waves in the fluid and membranes of the inner ear. The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea (of the inner ear).
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