The hearing and the maintenance of equilibrium organ went through a very long evolution process. One of the elements of effective functioning in the air was the forming of mechanisms intensifying the sound which reaches the inner ear. It was therefore, one of the conditions for transition to "life on the ground". Thus, the auricle is characteristic of mammals, the middle ear is observed in the case of the land vertebrates, whilst the vestibulocochlear organ is only to be found with the vertebrates. This work contains selected aspects of comparative anatomy of hearing and equilibrium organ in terms of its functions among certam chosen animal species. Some scientific and selfselected material (middle ear and inner ear of green frog, guinea pig, duck, macacus and dog) and the literature available were used.

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