The mule has its name mulus because it is yoked to the millstone and forced walk around it (in gyro molas) to turn the mill. It is the unnatural offspring of the mating of a female horse with a male ass. The hinny is a mule born of female ass and a male horse.

Bartholomaeus Anglicus uses a slightly different spelling (hinulus) of one of the names of the mule (hinnulus) to refer to a young deer, a fawn.

The mule is a beast of burden and so signifies those who are weighed down with the burden of vice and sin. As the mule is held by a bit and bridle so it goes where its master wants it to go, so should foolish men be restrained and forced to fast so that they will yield to God.

The droppings of the mule, pounded and burned with vinegar added, stops the flow of blood, and helps against the stings of scorpions.