大毘盧遮那成佛經疏 14.12

14.12

次舒散十指覆之，以二空相絞，即一切龍印也。因即以右加左上，是難陀龍。迴左加右，是小難陀也。如前九頭龍印，直申四指分為羽，是金翅印。凡地居多分單手作也。

Next, spread all ten fingers face downward and intertwine the two space fingers; this is the mudrā of all nāgas. Thereupon, placing the right on top of the left is the Nanda Nāga; turning the left to place it over the right is Upananda. As with the previous nine-headed nāga mudrā, extending four fingers straight out to form wings is the Garuda mudrā. Generally, those dwelling on earth are mostly performed with a single hand.