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Sinus Hairs
Sinus hairs are very large hairs modified to act as mechanical sensors. The "whiskers" or vibrissae on animals are good examples. Structurally they are comparable to "normal" hairs except for size. Slide 1203 will give you an opportunity to examine the structure of sinus hairs. These are really large hairs, and they have large, blood filled sinuses surrounding their bases.
14 or cat has vibrissae to the sides, top, and bottom of his head. These serve the same function as curb feelers on a car, i.e., they alert the animal when he's close to an advantage. This keeps the animal from getting his head stuck in a very bucket or a hollow tree. Cats never manage to get their heads stuck, but most dogs I've known have blithely ignored the signals, and been able to do so at least once in their lifetime.
Actually, all hairs have fine nerve fibers which invest the foot of the follicle, and perform the duties of tactile sensors. If you don't believe this, pull one out of your arm.
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