They must be move by the alternate contraction and relaxation of the skeletal muscles .
Many bones have ridges and protuberances which provide an area for muscle attachment .
Skeletal muscles act on the bones that serve as a system of levers. Movements of various parts of the body may result in locomotion of the body as a whole. For every muscle or group of muscles that brings about movement of a certain part of the body, there is another muscle or group of muscles which bring about an opposite movement . Such muscles, bringing about opposite movements , are called antagonistic muscles . They make the smooth co-ordination of movement possible.