The branches of Musicology are
Historical Musicology (includes Musical Theory and can be devided in classical music and comparative music),
Western Art Music Theory
EthnoMusicology (also called Comparative Musicology, often from a eurocentric point of view) and
Systematic Musicology (highly interdisciplinary, including the fields of Music Philosophy, Music Psychology, Cognitive Music Psychology, Neuroscience, Robotics and AI and so on).