THE BODY’S MUSCLES
The most prominent muscles in the body are the skeletal
muscles, which account for 40 to 45 per cent of body weight.
These muscles are defined as voluntary because they are
under conscious control; some important voluntary muscles
are indicated on the illustration below. In contrast, many
of the internal organs, such as the heart and the intestines,
consist partly or entirely of involuntary muscle, which is
not under conscious control.