For MATSYENDRASANA – SEATED SPINAL TWIST, from a seated position with your tailbone grounded evenly legs out as if ending Posterior Stretch. Cross one foot over the straight leg , placing the sole of the foot onto the floor. Rest the foot just outside of the other knee, or as close to the other hip as you can reach. If you would like a greater stretch you can bend the knee of the straight leg. Pull the sole of the foot toward your tailbone and hip. Make sure you are able to lengthen your spine and still be comfortable, otherwise you may want to straighten the leg back out. 
Inhale and take the arm opposite the leg with the sole of the foot resting on the floor up overhead. Exhale, twisting the spine to rest the elbow of that arm on the outside of the knee, looking over your shoulder. Place the other arm, palm down on the floor behind the body, pressing the fingers to the floor for leverage. Hold this pose for several breaths. Upon inhale lengthen the body and spine. Upon exhale relax into the stretch.
Repeat on the other side.
For an advanced variation of this posture grasp your hands together, binding, one arm through the bent knee and the other behind the back.
Benefits:
Seated spinal twist helps to maintain and restore normal spinal rotation by lengthening and releasing the muscles. Not only do the twists benefit the muscles, but also the soft tissue and vertebrae themselves. This pose literally “wrings” the organs, detoxifying and adding momentum to the digestive system, cleansing the body.
