Final answer:
The muscle's insertion is the part attached to movable elements like bones, while the origin is attached to fixed bones.
Step-by-step explanation:
The portion of the muscle that is joined to the movable attachments such as bones, movable muscle, or skin, is known as the muscle's insertion. On the other hand, the end of the muscle which is attached to a fixed (stabilized) bone is called the origin.
When the name of a muscle includes its attachments, the origin is always named first. For example, the sternocleidomastoid muscle has a dual origin on the sternum and clavicle, and inserts on the mastoid process of the temporal bone. Furthermore, muscles can also be named based on their actions, such as flexors or extensors.