Many muscles have the simple typical form of a belly tapering towards each end, as A, Fig. 30; others divide at one end, and are called two-headed, or biceps muscles, and there are even three-headed or triceps muscles. On the other hand, some muscles have no tendon at all at one end, the belly running right up to the bone to which it is fixed, and some have no tendon at either end. Sometimes a tendon runs along the side of a muscle, and the fibres of the latter are attached to it obliquely (B, Fig. 30); such a muscle is called penniform or featherlike, from a fancied resemblance to the vane of a feather ; or a tendon may run down the middle of the muscle (0), which is then called bipenniform. Sometimes a tendon is found in the middle of the belly as well as at each end (Fig. 31); such a muscle is called two-bellied or digastric. Running along the front of the abdomen, from the pelvis to the chest, on each side of the middle line, is a long muscle, the straight muscle of the abdomen (rectus abdominis) ; it is polygastric, consisting of four bellies separated by short tendons. Many muscles are not rounded, but form wide, flat masses, as those which lie beneath the skin on the sides of the abdomen.

Is the origin of a muscle under all circumstances its most fixed end? Give an example.

What is the simple typical form of a muscle? What is a biceps muscle? What a triceps? Have all muscles tendons at each end? At either end? Describe a penniform muscle. A bipenniform.