It is Preparing for a Gentle Birth: the Pelvis in Pregnancy
By · by Blandine Calais-Germain, Nuria Vives Pares
A wonderful book for midwives and doulas. Lots of great drawings and pictures.
http://www.barnesandnoble.com/w/preparing-for-a-gentle-birth-blandine-calais-germain/1111032443