What's the psoas?

We had a great time soaking up as much as we could from Brian Lam yesterday in his 4 hour anatomy workshop. He thought we might end early but we ended a little later than scheduled loosing track of time as we tried to expand our knowledge of asana and match it to the musculoskeletal system. With steady practice and memorization, he said, we'll all have greater understanding. I was impressed with how much some of our students already knew and how others picked up on the terminology so easily as we learned about origin/insertion points of muscles, the movers and shakers, or, uh, prime movers, antagonists and synergists in a pose. Good work everyone! And now as Pat so aptly said, it's time to bone up!