DOI link for Arabic linguistics
Arabic linguistics book
Semitic is divided into two large branches: East and West Semitic. East Semitic is the language of ancient Assyria and Babylonia, and was written in cuneiform characters; Western Semitic, after a period in which there were only dialects - Ugaritic, Amorite and, very probably, Eblaitic, when we shall know more about it - also divided into two branches: North-West Semitic, subdivided into Canaanite (Hebrew, Phoenician) and Aramaic (imperial Aramaic, Biblical Aramaic, Syriac, etc.), and South-West Semitic, subdivided into North Arabic - the language we shall be dealing with - and South Arabic, represented particularly by ancient Ethiopian (Geez).