一切經音義 25.437

25.437

（於此十二音外更添四字用補巧聲添文處用翻字之處輒不曾用用亦不得所謂乙上聲微彈舌乙難重用取去聲引力短聲力去聲長引不轉舌此四字即經中古譯魯留盧婁是也後有三十四字名為字母也）。

(Beyond these twelve sounds, four more characters are added to supply skillful sounds; they are used where text is added, but have never been used where characters are transcribed, nor could they be used. Namely: ṛ [乙 in rising tone, slightly flicking the tongue], ṝ [乙 repeated with difficulty, taking the departing tone lengthened], ḷ [short sound], and ḹ [departing tone, long and drawn out without rolling the tongue]. These four characters are the lu, liu, lu, and lou of ancient translations in the scriptures. Following them are thirty-four characters called the mother characters [mātṛkā]).