**Core Concept**
The cremasteric muscle is a fascial muscle that plays a crucial role in the regulation of testicular temperature. It is composed of smooth muscle fibers that contract and relax in response to changes in temperature, allowing the testes to ascend or descend to maintain optimal temperature.

**Why the Correct Answer is Right**
The cremasteric muscle is supplied by the cremasteric nerve, which is a branch of the genitofemoral nerve. The genitofemoral nerve arises from the lumbar plexus, specifically from the L1 and L2 nerve roots, and provides motor innervation to the cremasteric muscle. The cremasteric muscle also receives sensory innervation from the cremasteric nerve, which carries information from the testes to the spinal cord.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the obturator nerve primarily supplies the adductor muscles of the thigh, not the cremasteric muscle.
**Option B:** This option is incorrect because the femoral nerve supplies the muscles of the anterior thigh, including the iliopsoas and quadriceps, but not the cremasteric muscle.
**Option C:** This option is incorrect because the ilioinguinal nerve supplies the skin of the inguinal region and the cremasteric fascia, but not the cremasteric muscle itself.

**Clinical Pearl / High-Yield Fact**
The cremasteric reflex is a clinical sign that is used to assess the integrity of the cremasteric muscle and the genitofemoral nerve. The reflex is elicited by gently stroking the skin of the anterior superior iliac spine, which causes the cremasteric muscle to contract and elevate the testis.

**Correct Answer: D. Cremasteric nerve. Cremasteric muscle is supplied by the cremasteric nerve, a branch of the genitofemoral nerve.**