Final answer:
The sacrospinous ligament attaches from the last sacral and the first coccygeal segments to the ischial spine. It is crucial for the formation of sciatic foramina which allow for neurovascular passage. The sacrotuberous ligament, although similar in attachment region, connects to the ischial tuberosity instead.
Step-by-step explanation:
The ligament that attaches from the last sacral and the first coccygeal segments to the ischial spine is the sacrospinous ligament. This ligament spans the sacrum to the ischial spine and is integral in forming the greater and lesser sciatic foramina, which are important structures for neurovascular passage below the pelvis. While the sacrotuberous ligament also spans the sacrum, it specifically attaches to the ischial tuberosity, not the ischial spine, and thus, the correct answer to the question is: C. Sacrospinous ligament.