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The columella resides in the air-filled tympanic cavity of the middle ear. The footplate, or proximal end of the columella, rests in the oval window. Sound is conducted through the oval window to the interior of the otic capsule. [2] This motion ultimately stimulates sensory cells in the inner ear. [3]
The middle ear is the portion of the ear medial to the eardrum, ... it still has some ability to transmit vibrations to the inner ear. In many amphibians, ...
A partial middle ear formed by the departure of postdentary bones from the dentary, and happened independently in the ancestors of monotremes and therians. The second step was the transition to a definite mammalian middle ear, and evolved independently at least three times in the ancestors of today's monotremes, marsupials and placentals. [38]
In frogs and toads, the tympanum is a large external oval shape membrane made up of nonglandular skin. [2] It is located just behind the eye. It does not process sound waves; it simply transmits them to the inner parts of the amphibian's ear, which is protected from the entry of water and other foreign objects.
Later in development, the bone structure breaks loose from the jaw and migrates to the inner ear area. The structure is known as the middle ear, and is made up of the stapes, incus, malleus, and tympanic membrane. These correspond to the columella, quadrate, articular, and angular structures in the amphibian, bird or reptile jaw. [3]
Amphibians have unique inner ear structures. There are two sensory papillae involved in hearing, the basilar (higher frequency) and amphibian (lower frequency) papillae, but it is uncertain whether either is homologous to the hearing organs of lepidosaurs, archosaurs and mammals and it is uncertain when they arose. [9]
The middle ear consists of only the stapes bone and the oval window, which transfer vibrations into the inner ear through a reentrant fluid circuit as seen in some reptiles. Adults of species within the family Scolecomorphidae lack both a stapes and an oval window, making them the only known amphibians missing all the components of a middle ear ...
Air pockets around the stapes of Stanocephalosaurus have been hypothesized to act as resonance chambers, meaning that the spoon-shaped inner ear bone could be related to underwater hearing. This trait is possibly associated with early tetrapod evolution, which probably also appears on other members of this family and can act as a link to anuran ...