Smooth Muscle: One of two kinds of muscle, composed of
elongated spindle - shaped cells in muscles not under voluntary
control, such as the smooth muscle of the intestines, stomach, and
other visceral organs. The heart muscle is an exception because it
is a striated involuntary muscle. Smooth muscle fibers are shorter
than striated muscle fibers and are smooth in appearance. Known
also as involuntary muscle of unstriated muscle.