region of the brain that coordinates motor functions and muscle tone

In all vertebrates, including human beings, the cerebellum is one of the main divisions of the brain.

Position of the cerebellum (brain facing right)
A human brain, the cerebrellum is shown in purple (brain facing left)

The cerebellum works mainly to control balance and coordinate movement. It combines signals from eyes, muscle spindles, and ears with motor commands from the forebrain and helps to coordinate control of the body. More advanced regions of the human cerebellum may be crucial to language and mental dexterity. Bands of axons extend from the cerebellum into the pons.