Got a two-headed little mouse (on each arm)?

The full (Latin) name of the human biceps is "musculus biceps brachii" which means "two-headed little mouse of the arm."

"Two-headed" because the biceps is made up of two bundles, each with its own attachment point, or "head."

"Little mouse" because the muscle resembles the back of a mouse!  Indeed, the biceps appears to have given all muscles their name.

(And yes, the triceps has three "heads," and the quadriceps has four.)