Some acoustical properties of the otic bones of a fin whale

The otic bones in this report are the tympanic bulla, the periotic, and the three ossicles (malleus, incus, and stapes) of an adult fin whale (Balaenoptera physalus). The purpose was to determine if the periotic was denser than the other otic bones. It was found in one male adult fin whale that the density of all the otic bones is approximately the same, 2.50 kg/m3 with a maximum of 2.58. The lowest density was observed in the stapes (2.36). The sonic velocity seems to vary as the density but there also seems to be a structural effect. The maximum sonic velocity was 4.89 km/s in the malleus. The specific acoustic impedance was as high as 12.5 megarayles in the periotic. These values compare with those for human femur of 1.95 for the density, 3.73 for the sonic velocity, and 7.33 for the specific acoustic impedance. The ossicles weigh as much as 200 times as much as human ossicles. The density of whale ossicles are about ten percent greater than human ossicles. The mechanical natural frequency of the whale ossicles must be very low. The approximate uniformity of the properties of this whale's otic bones may be characteristic of the middle ear. The density of the otic bones of land mammals is less than for whales. The density of the horse petrosal (2.29 g/cc) is essentially the same as the density of adult human ossicles (2.23-2.27 g/cc). The high density of the otic bones for all mammals suggests it may be related to hearing acuity perhaps by increasing the specific acoustic impedance, which increases the acoustic contrast with the other body tissues.