Fascicle Arrangement in Skeletal Muscles

Skeletal muscles comprise fascicles, bundles of muscle fibers covered by a layer of dense connective tissue called perimysium.

Based on the arrangement of fascicles, skeletal muscles have four major classes—parallel, convergent, pennate, and circular.

Parallel muscles have fascicles placed along the long axis of the muscle and usually terminate in tendons on both ends.

These muscles can have a flat, straplike shape like the sartorius muscle of the thigh, or a spindle shape with an expanded belly, known as fusiform, like the biceps brachii muscle.

In convergent muscles, such as the pectoralis major, widespread fascicles converge at a common attachment point.

The pennate organization has three sub-types—unipennate, bipennate, and multipennate.

While unipennate muscles have fascicles on one side of a central tendon, bipennate muscles have fascicles on both sides.

In contrast, a multipennate muscle has oblique fascicles attached to multiple branched tendons. 

Lastly, the circular fascicle arrangement, also known as a sphincter, consists of concentrically arranged muscle fibers around an opening, such as the orbicularis oris muscle surrounding the mouth.