Degrees in Arts. In the mediæval ages the full course consisted of the three subjects which constituted the Trivium and the four subjects which constituted the Quadrivium:
The Trivium was grammar, logic, and rhetoric.
The Quadrivium was music, arithmetic, geometry, and astronomy. The Master of Arts was the person qualified to teach or be the master of students in arts; as the Doctor was the person qualified to teach theology, law, or medicine.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894