**Core Concept**
The ischial spine is a bony landmark on the posterior aspect of the pelvis, and its dorsal surface is crossed by several important structures. These include vessels and nerves that provide innervation and blood supply to the surrounding muscles and skin.

**Why the Correct Answer is Right**
The obturator nerve primarily runs along the medial aspect of the thigh, innervating the adductor muscles. It does not cross the dorsal surface of the ischial spine. In contrast, the pudendal nerve, which is responsible for innervating the perineal muscles, does cross the ischial spine. The internal pudendal vessel also traverses this region, providing blood supply to the perineal area. The nerve to obturator internus, which innervates the obturator internus muscle, crosses the ischial spine as well.

**Why Each Wrong Option is Incorrect**
**Option A:** The internal pudendal vessel does indeed cross the dorsal surface of the ischial spine, making this statement incorrect.
**Option B:** The pudendal nerve does cross the ischial spine, so this option is incorrect.
**Option D:** The nerve to obturator internus also crosses the ischial spine, making this statement incorrect.

**Clinical Pearl / High-Yield Fact**
The ischial spine is an important landmark for identifying the location of the pudendal nerve and its associated structures. This knowledge is crucial for surgeons and anesthesiologists performing procedures in the perineal region.

**✓ Correct Answer:** C. Obturator nerve