When looking at the hiragana ぬ (nu), ね (ne), and る (ru) one notices a small circle in the symbols. In fact that circle is the only difference when comparing them with the hiragana め (me), れ (re) and ろ (ro).
In the history of hiragana, is there any special reason that lead to this. And while I could see the relation of ね/れ and る/ろ (given that they sound similar), why are ぬ and め so different in their pronunciation?
(Image was taken, and slightly adjusted, from the manga “Mahoraba” by Kojima Akira)