Final answer:
The obturator foramen is formed by the edges of the obturator membrane, pubic, and ischium bones. The sacrospinous and sacrotuberous ligaments define both the lesser and greater sciatic foramina, which are important passages in the pelvic region.
Step-by-step explanation:
The obturator foramen is a large opening located in the anterior portion of the hip bone, situated between the pubis and ischium regions. This significant anatomical feature serves as a passage for nerves and blood vessels and provides a surface for muscle attachment. The margins of the obturator foramen are formed by the outer surfaces of the obturator membrane, the pubic bone, and the ischium. Additionally, it is largely filled by a layer of connective tissue. The lesser sciatic foramen is another critical structure in the pelvis, defined by the lesser sciatic notch of the hip bone, along with the sacrospinous and sacrotuberous ligaments. These ligaments aid in demarcating not only the lesser sciatic foramen but also the greater sciatic foramen, contributing to the complex architecture of openings on the posterolateral sides of the pelvis through which several anatomical structures pass to the lower limb.