Italicspart one and part two. The tutorial on the preceding ‘n’ branch also helps.
Like the ‘n’ branch, the ‘a’ branch is a family of italic letters which all derive from a certain root (‘a’). The ‘a’ branch sprouts off of the side of the ‘n’ branch, and the ‘u’ and the ‘a’ form the junction between the two. In this way, the ‘a’ branch can be thought of as the second stage of italic design, though the design process is quite similar to that of the previous branch.
The letter a
Unlike the roman ‘a’, the italic ‘a’ has only a single bowl and stem, much like a ‘d’ without its ascender.