Final answer:
The pudendal nerve enters the perineum through the lesser sciatic foramen, a pelvic opening formed by the lesser sciatic notch of the hip bone, the sacrospinous ligament, and the sacrotuberous ligament.
Step-by-step explanation:
The pudendal nerve enters the perineum through the lesser sciatic foramen. The lesser sciatic foramen is a pelvic opening that is formed by several anatomical structures: the lesser sciatic notch of the hip bone, the sacrospinous ligament, and the sacrotuberous ligament. It is a smaller and more inferior opening compared to the greater sciatic foramen, which is another significant opening in the pelvis formed by the greater sciatic notch of the hip bone, the sacrum, and the sacrospinous ligament. The greater sciatic foramen allows the passage of structures such as the sciatic nerve and other muscles, nerves, and blood vessels that travel to the lower limb.