Unlike the equator and the Tropic of Cancer and the Tropic of Capricorn, the Prime Meridian and all lines of longitude are completely imaginary lines and have no significance with regard to the Earth or to its relationship with the sun.
Black hairy tongue typically results when projections on the tongue called papillae grow longer and don't shed like normal. This makes the tongue look hairy. Debris, bacteria or other organisms can collect on the papillae and result in discoloration. The cause of black hairy tongue can't always be determined.
hairy tongue a benign condition of the tongue characterized by hypertrophy of the filiform papillae that gives the dorsum of the tongue a furry appearance. The color of the elongated papillae varies from yellowish white to brown or black, depending upon staining by substances such as tobacco, foods, or drugs.