In nearly all cases the voluntary muscles carry out their special functions with the co-operation of the skeleton ; most of them are joined to bones at each end and when they contract move the bones, and, secondarily, the soft parts attached to these. When muscles move bones the latter are almost invariably to be regarded as levers whose fulcra lie at the joint where the movement takes place. Examples of the three forms of levers recognized in mechanics are found in the human body.

In what respect are all muscles alike? Have all muscles the same uses? Give instances of the employment of muscles for different purposes. What is meant by the special physiology of a muscle? What by its general physiology?

With what do the voluntary muscles co-operate? To what are the ends of nearly all muscles attached? What happens when a muscle contracts?