A cat has about twenty-four movable vibrissae ("whiskers"), in four sets on each upper lip on either side of its nose (some cats may have more). There are also a few on each cheek, tufts over the eyes, bristles on the chin, the cat's inner "wrists", and at the back of the legs.[10] The Sphynx (a nearly hairless breed) may have full length, short, or no whiskers at all. The structure of the brain region (barrel cortex) which receives information from the vibrissae is similar to that found in the visual cortex which permits the cat to create a three dimensional map of its surroundings. This doesn't mean that sensing with vibrissae is a type of vision. It is still a touch sensation and environmental information is built up incrementally (in small steps).[11][12][13][14] Vibrissae aid sensation and navigation. The upper two rows of whiskers are able to be moved independently from the lower two rows for greater precision during measurement. A cat's whiskers are more than twice as thick as ordinary cat hairs, and their roots are three times deeper in a cat's tissue than other hairs. They have numerous nerve endings at their base, which give cats extraordinarily detailed information about nearby air movements and objects with which they make physical contact. They enable a cat to know that it is near obstacles without it needing to see them. Whiskers also aid in hunting. High speed photography reveals that when a cat is unable to see its prey because it is too close to its mouth, its whiskers move so as to form a basket shape aroun

its muzzle in order to precisely detect the prey's location.[15][16] A cat whose whiskers have been damaged may bite the wrong part of its prey indicating that they provide cats with detailed information about the shape and activity of its prey. Whiskers may also help cats to detect scents more readily by directing air currents to their nose and mouth.[citation needed] Whiskers are also an indication of the cat's attitude. Whiskers point forward when a cat is inquisitive and friendly, and lie flat on the face when the cat is being defensive or aggressive. Vibrissae (singular: vibrissa), or whiskers, are specialized hairs usually employed for tactile sensation.[1] The term may also refer to the thick hairs found inside human nostrils, but these are not true whiskers, as humans lost function in an enhancer of the androgen receptor gene that controls the growth of whiskers about 700,000 years ago.[2] Vibrissae hair grow around the nostrils, above the lips, and on other parts of the face of most mammals, and all primates except humans,[3] as well as on the forelegs and feet of some animals. The presence of mystacial (where a moustache would be) vibrissae in distinct lineages (Rodentia, Afrotheria, Marsupials) with remarkable conservation of operation suggests that they may be an old feature present in a common ancestor of all therian mammals.[4] Indeed, some humans even still develop vestigial vibrissal muscles in the upper lip,[5] consistent with the hypothesis that previous members of the human lineage had mystacial vibrissae.