Structural and functional organization of sound generation and sound perception organs in dolphins

Abstract

comparative morphological study of the sound-generation and sound-perception organs in dolphins was conducted. The exact conformity of the lateral edge of premaxillary sacs with the size and outer configu- ration of ventral valves having lip-shaped apophyses, the location of inferior vestibules and the entries to the nasofrontal and accessory sacs, and also some other peculiarities indicate that the complexity and fineness of organization of this part of air pathways are connected with sound - generation and are not necessary for breathing. The role of this complex in sound generation is also manifested by the fact, that the dolphins, which do not have it (river dolphin, porpoise), demonstrate much poorer sound repertoire, compared to the species, which possess it (white whale, bottlenose and common dolphins). In echolocat- ing mammals, the substantial growth of the cochlea's sizes in comparison with the sizes of the vestibular apparatus, as well as other features in the structure of the cochlear canal and the cells of the organ of Corti serve as the cochlea's adaptations to the perception of frequencies of a wide range, including ultrasound (dolphins, bats). At the same time, the large cochlea and the extraordinarily small size of the vestibular apparatus in absolute hydrobionts, which posses varied orientation of hearing, can be considered to be the adaptation of the inner ear to aquatic life, as the hearing of aquatic mammals dominates among distant analyzers, thus providing the survival of these animals while dwelling in an aquatic environment.