Now, if you look at one of these under a microscope you find that it is made of still finer fibres, which are much smaller than the threads of a spider's web.

One of these smallest threads is called a _muscular fibre_.

Many thousands of muscular fibres are required to make a muscle.
[Illustration: MUSCULAR FIBRES.] ~5.~ Most of the muscles are made fast to the bones.

Generally, one end is attached to one bone, and the other to another bone.

Sometimes one end is made fast to a bone and the other to the skin or to other muscles.
~6.