Anatomy and function of the cetacean ear.

Abstract

At the present time the sounds emitted by cetaceans and consequently their sense of hearing are the subject of a considerable amount of investigation. The remarks that follow are in anticipation of a more detailed account of the cetacean ear which the writers have completed for the Bulletin of the British Museum (Natural History). In order to clarify the hypothesis arrived at, a brief summary of the anatomical features involved is necessary (in connexion with which reference to figures 88 to 90, plates 10 and 11 should be made). The external auditory m eatus is a continuous narrow tube in the toothed cetaceans (figure 88). In the whalebone whales (figure 89) it is usually closed for some p art of its length im mediately internal to the blubber layer, The m eatus is lined by a pigmented extension of the epidermis. Surrounding the fining layer is a fibro-elastic sheath, the fibres of which run predom inantly along the length of the meatus. Surrounding this sheath again is a fibro-cellular structure in which a thin stratum of circular constrictor muscles has been observed. Enveloping the whole of this area and adhering to the bones is a great mass of dense, white fibrous tissue about 30 cm in thickness with tough, unyielding fibres forming a close randomly orientated reticulum throughout the entire mass. The meatus is thus enclosed in a tunnel formed dorsally of bone and ventrally of white fibrous tissue.