Describe the three forms of pennate muscles and give an example of each.

The three forms of pennate muscles are unipennate, bipennate, and multipennate. In a unipennate muscle, fascicles insert on only one side of the central tendon, as in the extensor digitorum longus of the leg. In a bipennate muscle, fascicles insert on opposite sides of the tendon, giving a feather-like appearance, as in the rectus femoris of the thigh. A multipennate muscle looks like many feathers side by side inserting into one large tendon, as seen in the deltoid muscle of the shoulder.

Pennate muscles have short fascicles that attach obliquely to a central tendon running the length of the muscle. The unipennate form has fascicles inserting into only one side of the tendon, exemplified by the extensor digitorum longus muscle of the leg. The bipennate form has fascicles inserting from opposite sides of the tendon, making the muscle look like a feather; the rectus femoris of the thigh is an example. The multipennate form resembles many feathers placed side by side, with all their quills inserting into one large tendon; the deltoid muscle, which forms the roundness of the shoulder, is multipennate. Because the arrangement packs in many fibers, bipennate and multipennate muscles shorten little but are powerful.