**Core Concept**
The lymphatic drainage of the urethra is a crucial aspect of urogenital system anatomy. The spongy urethra, also known as the penile or penile urethra, is a part of the male urethra that runs through the corpus spongiosum of the penis.

**Why the Correct Answer is Right**
The lymphatic vessels from the spongy urethra drain into the deep inguinal lymph nodes. This is because the lymphatic vessels of the penis, including the spongy urethra, follow the path of the venous drainage, which is into the deep inguinal nodes. The deep inguinal lymph nodes are located along the femoral vein and are responsible for draining the lymph from the lower limb, pelvic organs, and the anterior abdominal wall. The lymphatic drainage of the spongy urethra is an important aspect of the body's defense mechanism against infections.

**Why Each Wrong Option is Incorrect**
* **Option A:** Superficial inguinal lymph nodes - These nodes are located along the saphenous vein and primarily drain the skin of the lower limb and the gluteal region. While they do receive some lymph from the penis, they are not the primary site of drainage for the spongy urethra.
* **Option B:** Internal iliac lymph nodes - These nodes are located along the internal iliac artery and primarily drain the pelvic organs, including the urinary bladder, but not the spongy urethra.
* **Option C:** External iliac lymph nodes - These nodes are located along the external iliac artery and primarily drain the lower limb and the abdominal wall, but not the spongy urethra.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the lymphatic drainage of the penis, including the spongy urethra, is into the deep inguinal lymph nodes. This knowledge is crucial for surgeons and clinicians to identify the correct drainage pattern in case of lymph node metastasis or infection.

**Correct Answer:** C.