大毘盧遮那成佛經疏 14.10

14.10

次舒左手，而令曲如承髑髏之狀，當胸前仰之，是遮文荼印也。左手以空捻地水甲上，而申火風並竪之，即涅哩底刀印也。

Next, extend the left hand and curve it as though holding a skull-cup, turning the palm upward before the chest; this is the Cāmuṇḍā mudrā. With the left hand, pinch the nails of earth and water with space, and extend fire and wind erect side by side; this is the Nirṛti Sword mudrā.