Cochlea of the dolphin, Tursiops truncatus: the basilar membrane.

In the dolphin Tursiops truncatus, the basilar membrane over its course its course from basal to apical ends shows a systematic variation in width and in the manner and rigidity of its suspension. The suspension is by bony laminae on both the outer and inner edges in the basal region, and by progressively less rigid attachments in the more apical regions, until near the apex the membrane is held only by connective tissue. The basilar membrane shows an unusual variation in width of 14 times, ranging from an astonishingly small value of 25 mum at the basal end to a value toward the apex of about 350 mum. This structural variation is in harmony with the extension of sensitivity of the dolphin ear into the very high frequencies, and suggests unusual capabilities of pitch discrimination in this high range.