This section is from the book "Animal Physiology: The Structure And Functions Of The Human Body", by John Cleland. Also available from Amazon: Animal Physiology, the Structure and Functions of the Human Body.
Unstriped Muscle is, for the most part, found diffused among the other tissues of organs, into the formation of which it enters, or lying in strata. Striped muscle, for the most part, is gathered into definitely limited organs called muscles, which have a distinct origin and insertion, and usually a certain amount of tendon in their construction. The extent of action of a muscle depends on the length of its fibres, while its strength of action is in proportion to the number of them. When therefore a muscle consists of few fibres running lengthwise from origin to insertion, it is useful rather for the extent of the movement which it serves, than for the force which it gives to it. But when great resisting power is required in a muscle, its tendons extend through its substance, and its muscular fibres are short and numerous, passing obliquely from one prolongation of tendon to another: thus in the soleus, one of the muscles of the calf already referred to (p. 51), the fibres are arranged in four oblique sets, and are none of them more than about an inch in length; so that the muscle is incapable of approximating its attachments more than an inch, but can exert in its limited range an enormous force, and is thus well adapted to sustain the weight of the body in standing.