Body Organs

Hair are thin growths, that protrude like filaments from the skin of mammals. Different kinds of mammals range widely in their degree of harness. Some have dense growths called are only sparsely haired, such as elephants, and humans. A few mammals, such as the whale, are hairless except for a small number of bristles. Hair is now unique to mammals, although some lizards show hairlike growths, but it probably first appeared on extinct mammal-like reptile ancestors. Different kind of hair have different functions. Most obviously, the luxuriant furs of mammals in polar and temperate regions serve as body insulation. Insulating furs, often have two coats, a thicker underfur of fine hairs and a coarser cutter coat of guard hairs. More specialized hairs are also seen on many mammals, especially on the faces of carnivores and rodents . These hairs, called vibrissae, are surrounded at their base by sensory nerve fibers. They serve the animals as touch organs, helping them to measure their s...

Facial Muscles The muscles used in facial expression are unique in that they are attached to various parts of the facial skin. They surround and radiate from the vital orifice of the face; the mouth, nostrils, eyes and ears. Some muscles open these orifices write, others narrow or close them. Muscles of Mastication Four large muscles on each side move the jaw. The temporal (in the temple) and the masseter (on the side of the jaw) can be felt when a person bites forcibly. The other muscle help provide the motions needed for grinding food between the molars. Tongue, Swallowing, and Speech Muscles The tongue is almost all muscle, and it is capable of very precise, complicated, and elaborate movements. In eating, the tongue moves food around, in swallowing, it pushes food into the throat, and in taking, it articulates the sounds coming from the larynx. Once food enters the pharynx (the throat) it is moved down into the esophagus by waves of muscle contraction. Special sets of muscl...