Stretching the Left Piriformis Muscle,

http://www.drbackman.com/piriformis-muscle-stretch.htm

Stretching the Left Piriformis Muscle, A New Way and the Traditional Piriformis Muscle Stretch Are Pictured.
Sitting Piriformis Stretch, if you want to find this deep hip muscle in the buttocks:

1. Sit Up Straight
2. Cross your legs and lean forward.
(While sitting at a seminar and had crossed my legs in a figure 4 then leaned forward feeling a stretch, looked down to see what appeared to be a new Piriformis stretch.)

To Do A Quick Check To See How Tight Your Hip Muscles / Joints Are, Just Sit Up & Cross Your Legs As In The Picture On The Left. If Your Knee/Lower Leg Is at a Similar Height/Level, This Is Good; The Higher Your Knee, The Tighter Your Hip Joint. Also Compare Your Left and Right knees As You Relax In This Position. (The Nice Thing About The Stretch On The Left Is, You Can Be In A Meeting, Cross Your Legs, Lean Into the Conversation and Everybody Assumes That You Are Engrossed, But You Are Just Doing Your Stretches.) Remember, if there is any pain, BACK OFF or stop. Hip Mobilization Exercise Here

More information here:
http://www.spineuniverse.com/displayarticle.php/article130.html