. Bulletin of the British Museum (Natural History). HEARING IN CETACEANS 109 Several descriptions exist of the structure and course of the external auditory meatus in the Cetacea. The absence of an external pinna was noted by some of the earliest writers ; Rondelet (1554) appears to have been the first to notice the external aperture of the ear. In the smaller odontocetes it is less than a millimetre in diameter and can only be detected by careful examination of the region behind the eye. The aperture in the larger, baleen whales is lenticular in shape, usually concealed in a groove and measur
. Bulletin of the British Museum (Natural History). HEARING IN CETACEANS 109 Several descriptions exist of the structure and course of the external auditory meatus in the Cetacea. The absence of an external pinna was noted by some of the earliest writers ; Rondelet (1554) appears to have been the first to notice the external aperture of the ear. In the smaller odontocetes it is less than a millimetre in diameter and can only be detected by careful examination of the region behind the eye. The aperture in the larger, baleen whales is lenticular in shape, usually concealed in a groove and measures about i cm in its larger Fig. 27. Diagram of a dissection of the ear of Globicephala melaena (cf. Plate 49). Ventral view, left side. The course of the meatus in Globicephala melaena from the surface of the body to the external aspect of the tympanic membrane is shown in Text-fig. 27. The tube (eam) passes inwards more or less horizontally for about 2 â 5 cm, then dorsally and caudaUy in a sharp bend which occupies another 2-5 cm, rounding again to its original direction to its termination at the tympanic membrane. The mean axis of the meatus is at right angles to the long axis of the body. According to LiUie (1915), in Megaptera novaeangliae, from the external orifice " a tube about i/io in. in diameter traversed the blubber which was about 3^ in. thick in this region. The tube was continued through the underlying tissue for about 2 in. and gradually decreased in diameter until it ended bhndly. The meatus was. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(NH)
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