The cochlea in gerbilline rodents.

The inner ears of 5 different gerbil species are compared on the basis of cochlear microphonic recordings, serial sections and computerized quantitative reconstructions of the cochleae and their specific morphological structures. The hearing range of most gerbils is below 20 kHz. Some species are extremely sensitive in the frequency range of 1-4 kHz. This special sensitivity is reflected in, among other features, the following cochlear structures and their suggested functions: (1) the rapid width increase of the basilar membrane in the basal portion of the cochlea provides additional space for the representation of lower frequencies at the expense of higher frequencies; (2) the large hyaline mass and the cells of Claudius and Hensen in the medial and apical portions of the cochlea influence the vibratory properties of the cochlear partition, and (3) the specialized structures of the cochlea may be an adaptation to the acoustical environment in arid habitats.