Dhyana Mudra.

This mudra signifies meditation. Both hands are in the lap with palms upward. The right hand is on top of the left hand. The Buddha is most seated in the half-lotus posture (sometimes called 'yoga', 'Indian', 'Buddha' posture). Some images display the Buddha in the so-called adamantine (diamond, or full-lotus) posture with tightly crossed legs, so that the soles of both feet are visible.
The Bodhisattva makes a vow and is determined not the leave the spot (where he is sitting on the grass) until he achieves enlightenment. The Boddhisattva determines to find the cause of suffering and its cessation.

Dvaravati art - Buddha, protected by Naga in meditation posture. 8 - 11 th century A.D. Found at Si Mahosot, Prachinburi province. Now in the National Museum, Bangkok.

Meditating Sitting in the yoga posture. Note the right leg on top of the left, the right hand on top of the left hand. Buddha image presently at Phra Pathom Chedi.

Sitting Buddha image, with the gesture of Meditation. In the style of the Chiang Saen period. Found at Chiang Saen, Chiang Rai province. Image present in the cloister of the Ubosoth at Wat Benchamabophit, Bangkok.

Buddha in Meditation, sheltered by Naga. Khmer art, Bayon Style (1177-1230 A.D.) National Museum Prachinburi