Middle Ear Functional Morphology of the Domestic Cat (Felis catus) and the Domestic Sheep (Ovis aries): A Comparative Study with Two Echolocating Mammals (Globicephala macrorhynchus and Tadaridabrasiliensis mexicana - Abstract
Sound localization in nature is important especially for those creatures who hunt in the dark. Swimming and flying animals do this three-dimensionally, as opposed to animals living on the ground that mainly need to localize sound in a horizontal plane. Earlier studies have suggested directional asymmetry between the left and right middle ears in two mammals echolocating in three dimensions, the short-finned pilot whale (Globicephala macrorhynchus) and the free-tailed Mexican bat (Tadarida brasiliensis mexicana). In them, the asymmetry is likely to improve localization of incoming sounds, especially in the “zone of acoustic ambiguity”, in the vertical plane in front and behind the head. Here we study whether this kind of asymmetry can be found in the middle ears of two terrestrial mammals, the domestic cat (Felis catus), a carnivore, and the domestic sheep (Ovis aries), an artiodactyl and a close relative of cetaceans. We provide measurements on the masses and lengths of the ossicles, and on the stapes footplate area and applied a t-test to the data. We found that asymmetry was not present between the left and right middle ears in the cat or in the sheep. We provide qualitative photomicrographs of sheep and cat middle ear dissections, obtained using Leica Microsystems stacked image technology, with accompanying commentary. Structure and function is discussed and the likely contribution of the tensor tympani muscle of these two species in the acoustic reflex, and in transmission of high frequency sound from the middle ear to the perilymph of the vestibule, is highlighted.