The ear of the chameleon: Chamaeleo senegalensis and Chamaeleo quilensis

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Abstract
The chameleon ear presents special problems because of variations of structure from the usual lizard pattern: there is no external ear opening and no visible tympanic membrane, and the round window of the cochlea is usually said to be lacking.Measurements of auditory sensitivity in terms of the electrical potentials of the cochlea were carried out in two species, Chamaeleo senegalensis and Chamaeleo quilensis. The results indicated poor sensitivity in comparison with lizards in general, yet the performance was not far below that found in many species with conventional sound‐conducting systems. The frequency range extended from 100 to 10,000 cps, with the best sensitivity in the region of 200 to 600 cps.Experiments were carried out to investigate the operation of these ears in response to aerial sounds and mechanical vibrations. The observations indicated that aerial sounds are received by a special surface, the pterygoid plate, embedded in the tissues at the side of the head. This system resembles that of snakes, in which a detached quadrate bone serves as a receptive surface.The round window problem is not yet solved, but the suggestion is made that there is a path of pressure discharge from the scala tympani to the air of the middle ear cavity by a circuitous route, through the tympanic recess and a series of small spaces and blood vessels traversing the glossopharyngeal foramen. The frictional resistance of such a hindered pathway of discharge could account for the poor sensitivity of these chameleon ears.

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