SOME PERIPHERAL AUDITORY CHARACTERISTICS OF THE MARSUPIAL BRUSH-TAILED POSSUM, TRICHOSURUS-VULPECULA

Some anatomical and physiological aspects of the peripheral auditory system were examined in anesthetized brush‐tailed possums Trichosurus vulpecula and compared with those in the cat. Cochlear microphonic potentials (CM) in response to tones of varying frequency and intensity were recorded at the round window. The cochlea of Trichosurus has a typically mammalian appearance, with three and one‐half turns and a basilar membrane approximately 17 mm in length upon which sit three rows of outer and one of inner hair cells. Three middle ear ossicles, including a delicate stapes of columelliform appearance, are housed in a cavity adjacent to a spongy mass of bone. The latter surrounds the round window and is quite unlike the bullae of many eutherian mammals. Round window recordings revealed that CM potentials of the possum rarely attained magnitudes, for any tone, in excess of 500 μV and were always 10–25 dB less in amplitude than CM of the cat at a given frequency and intensity. The threshold intensities required to elicit a 50 μV CM at frequencies between 0.4 kHz and 10 kHz were smaller for the cat than the possum, but a slightly greater sensitivity was shown by the possum between 0.1 kHz and 0.4 kHz. Peripheral auditory characteristics of the marsupial brush‐tailed possum thus appear to have some features in common, and others at variance, with commonly‐studied placental mammals. Copyright © 1979 Wiley‐Liss, Inc., A Wiley Company