They are called extrinsic because the muscle belly is located on the forearm.

The propatagialis tendo longus has no distinct muscle belly.

The tendon of the index finger often has a separate muscle belly.

Both heads arise on the scapula and join to form a single muscle belly which is attached to the upper forearm.

Both heads join on the middle of the humerus, usually near the insertion of the deltoid, to form a common muscle belly.

This allows more space for the inflamed muscle belly, thus, relieving pain/pressure.

The fleshy, central part of a skeletal muscle (also known as a "muscle belly")

It is composed of a thin muscle belly and a long thin tendon.

This layer is 1 mm thick and contains fibers that are oriented obliquely to the long axis of the muscle bellies.

The muscle belly is approximately 2-4 inches long, and is absent in 7-10% of the human population.