2. Cetacean Ears
73
The interossicular joints are not fused nor are they apparently stiffened by
auxiliary ligaments. While there are no clear patterns of ossicular ligaments
in mysticetes, this does not preclude them. Ossicular ligaments and muscles
have been reported but the descriptions are inconsistent (e.g., Hyrtl1845;
Boenninghaus 1903; Fraser and Purves 1960). Long post-mortem times
and poor preservation are common in baleen material and the inconsistencies could be the result of post-mortem change rather than normal
variations or species differences. The ossicles, with the exception of a stalked
malleus, are not fused to the bulla. There is no indication of stapedial fusion
or calcification of the annular ligament. As noted earlier, the tympanic
bulla scales with animal size and is double the volume of the periotic
bulla. Thus, the mysticete middle ear consists of a large, open cavity with
massive ossicles that are loosely joined; i.e., a characteristically lowfrequency ear.
Exactly how "massive" are whale ear bones? Lees et al. (1996) measured
weight, density, and sonic velocities of relatively fresh fin whale and human
ossicles and periotics (Table 2.3). Ossicular weights from a mixture of formalin preserved and dehydrated ears were reported also by Norris and
Leatherwood (1981). Lees et al. found that although fin whale tympanic,
periotic, malleus, and incus bones had weights 50 to 250 times adult human
equivalents, the densities were only 10% greater than in humans (Table
2.3). The density of the porpoise periotic was 2.7 gm/cc or 10% greater than
a fin whale periotic and 20% greater than the human temporal bone. Lees
et al. calculated that the specific acoustic impedance of the porpoise periotic (14.09 megarayles) is nearly twice that of a human femur and 20%
greater than that of an average fin whale periotic (11.7 megarayles). They
concluded that three inter-related parameters, high density, high sonic
velocity, and high specific acoustic impedance, increase acoustical contrast
of the periotic with the other bones, and, like Reuter et al. (1998) for the
elephant, concluded also that the large mass of mysticete ossicles suggests
a low ossicular chain resonance.
5.2.3 Cetacean Middle Ear Dysfunction: The Debate
Reysenbach de Haan's remark (1956) that "all possible efforts have been
made (unsuccessfully) to eliminate the middle ear mechanism ... as a
sound transmission system" is still a fair summary of the state of the whale
middle ear debate. The fundamental issue is that in air, the external and
middle ear act more efficiently than other channels to deliver acoustic
power to the oval window, which induces cochlear motion and differential
movement of the round window (for detailed discussions see Rosowski
1994; Yost 1994). If tissues in contact with the ear and both cochlear
windows are all equally efficient, then no differential motion of the cochlear
windows occurs and the inner ear membranes are not displaced. Many
soft tissues have impedances close to sea water. The questions that are
73
The interossicular joints are not fused nor are they apparently stiffened by
auxiliary ligaments. While there are no clear patterns of ossicular ligaments
in mysticetes, this does not preclude them. Ossicular ligaments and muscles
have been reported but the descriptions are inconsistent (e.g., Hyrtl1845;
Boenninghaus 1903; Fraser and Purves 1960). Long post-mortem times
and poor preservation are common in baleen material and the inconsistencies could be the result of post-mortem change rather than normal
variations or species differences. The ossicles, with the exception of a stalked
malleus, are not fused to the bulla. There is no indication of stapedial fusion
or calcification of the annular ligament. As noted earlier, the tympanic
bulla scales with animal size and is double the volume of the periotic
bulla. Thus, the mysticete middle ear consists of a large, open cavity with
massive ossicles that are loosely joined; i.e., a characteristically lowfrequency ear.
Exactly how "massive" are whale ear bones? Lees et al. (1996) measured
weight, density, and sonic velocities of relatively fresh fin whale and human
ossicles and periotics (Table 2.3). Ossicular weights from a mixture of formalin preserved and dehydrated ears were reported also by Norris and
Leatherwood (1981). Lees et al. found that although fin whale tympanic,
periotic, malleus, and incus bones had weights 50 to 250 times adult human
equivalents, the densities were only 10% greater than in humans (Table
2.3). The density of the porpoise periotic was 2.7 gm/cc or 10% greater than
a fin whale periotic and 20% greater than the human temporal bone. Lees
et al. calculated that the specific acoustic impedance of the porpoise periotic (14.09 megarayles) is nearly twice that of a human femur and 20%
greater than that of an average fin whale periotic (11.7 megarayles). They
concluded that three inter-related parameters, high density, high sonic
velocity, and high specific acoustic impedance, increase acoustical contrast
of the periotic with the other bones, and, like Reuter et al. (1998) for the
elephant, concluded also that the large mass of mysticete ossicles suggests
a low ossicular chain resonance.
5.2.3 Cetacean Middle Ear Dysfunction: The Debate
Reysenbach de Haan's remark (1956) that "all possible efforts have been
made (unsuccessfully) to eliminate the middle ear mechanism ... as a
sound transmission system" is still a fair summary of the state of the whale
middle ear debate. The fundamental issue is that in air, the external and
middle ear act more efficiently than other channels to deliver acoustic
power to the oval window, which induces cochlear motion and differential
movement of the round window (for detailed discussions see Rosowski
1994; Yost 1994). If tissues in contact with the ear and both cochlear
windows are all equally efficient, then no differential motion of the cochlear
windows occurs and the inner ear membranes are not displaced. Many
soft tissues have impedances close to sea water. The questions that are