Vignana Bhairava Tantra - 48

Just empty space within

Dehantare Tvagvibhagam Bhitti Bhootam Vichintayeth
Nakinchit Antare Tasya Dhyayanadhyeya bhagbhaveth

One of the methods is to contemplate on the surface of the skin as a partition separating the space outside and inside. There is nothing within the body of yours, except space. Meditating thus, one becomes in tune with the space within that cannot be meditated upon.
- Swahilya Shambhavi.

Vignana Bhairava Tantra - 47

Nothing inside, but space

Sarvam Dehagatam Dravyam Viyadvyaptam Mrigekshane
Vibhavayet Tatastasya Bhavana sa Sthira Bhaveth

Oh one with eyes as a gazelle! Contemplate in this way, that all the parts inside the body is contained in and permeated and surrounded by space. In this manner, when the mind contemplates, it becomes as steady and still like space itself. - Swahilya Shambhavi

Vignana Bhairava Tantra - 46

You are empty within

Tanoodeshe Shoonyataiva Kshanamatram Vibhavayeth
Nirvikalpam Nirvikalpo Nirvikalpaaswaroopabhaat

Now this seems so easy to meditate upon something for just a moment. Consider or imagine, just for a moment, that there is only space inside this body. Imagine just a while that within your outer structure, covered totally by the skin, there is only empty space. This thought leads you to a thoughtless state of mind and you, the contemplating mind becomes that form of void. - Swahilya Shambhavi.