हठयोग प्रदीपिका (योगी स्वात्माराम - ज्योत्स्ना टीका सहित सटीक)

42 HAṬHAYOGAPRADĪPIKĀ
29. This is Mahāvedha which, with practice,
confers great siddhi-s. This staves off wrinkles, grey
hair and trembling [consequent on old age], and the
best of practitioners devote themselves [to it].
30. These three, that ward off old age and death,
increase the [gastric] fire and confer siddhi-s such as
aṇiman, should be most carefully kept secret.
31. These are performed in eight different ways,
every day at every yāma (three-hour period). They
confer at all times the fullness of virtue and destroy the
accumulation of sin (pāpa). Those who are well guided
[by the teacher] in these should practise them gradually.
32. The KHECARĪ [is described]: When the tongue
is turned back and enters the cavity leading to the
skull, and the eyes are fixed between the eyebrows,
this is Khecarī-mudrā.
33. By cutting, shaking and stretching, the tongue
should be gradually elongated, till it touches the middle
of the eyebrows. Then the Khecarī is successfully
accomplished.
The procedure for cutting is described in the following verses.
Shaking means taking hold of the tongue with the fingers and
moving it to left and right. Stretching means taking hold of the
tongue and drawing it as one does the udders of a cow in
milking it.
34. Taking a smooth, clean knife, very sharp like
the leaf of the milkhedge plant, cut to a hair's breadth
[the fraenum or tender membrane that connects the
tongue with the lower part of the mouth].