Elephants can Hear Through Foot

Elephants possess two possible ways of detecting
vibrations. One is through the ear; as we hear through our
ears. The other one is not connected with the ear. Often,
they use both. Sound produced by the animal is conducted
both by air as well as through the ground. The ground
vibrations travel through the bones that goes up through
the feet, then the legs, shoulder and finally into the middle
ear cavity.

Middle ear bone in the elephants is relatively enlarged,
especially the malleus. Additional mass of this bone
facilitates independent oscillations of the middle ear
bones. Bone conduction actually by-pass eardrum step.

In addition to the larger ear bones, the dense fat in the
foot pad may also facilitate the bone conduction route.  In
addition, elephant may also use the sphincter like skeletal
muscle which is situated at the opening of the ear canal.

In this connection, it is worth knowing that many mammals
detect vibrations by means other than the ear. To site an
example, primates have three different vibration detecting
cells found in the lips, hands, feet and the intestinal muscle
lining. Each can detect the range.

Similar receptors are also found in the tips of Asian
elephants' trunk, that is similar to that seen in the lips of
primates. Snout of star-nosed mole, paws and knees of
cat, knees of kangaroos, beak skin and knees of birds are
some of the other examples.

Vibration sensitive cells of elephants in the feet is similar to
those found in the trunk. These cells are  onion like, with
several layers, surrounding a nerve. In the foot, these cells
are seen at the edges, mostly at the heel and toe. That
may be the reason why elephants move back and forth on
its front foot when seismic waves are detected.

The time difference between the hearing through the ear
and foot may help the animal to assess the distance from
where the sound originated. This can be explained by the
usual analogy of time gap between lightning and thunder.

                                                                    
November 2007
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