Here is a great resource for those of you that are curious about "what lies beneath the surface", especially if you are a ball roller, this way you can have an idea of what you are doing. Scroll down the article to dive deeper into the pelvis, to view the attachments of the psoas from multiple angles. it's quite something. enjoy.

http://medicfrom.com/publicpress/Massage/Basic_Clinical_Massage_12.html