**Core Concept**
The lymphatic drainage of the glans penis is a crucial aspect of urology and anatomy, involving the **lymphatic vessels** and **lymph nodes**. The glans penis, being a part of the external genitalia, has a unique lymphatic drainage pattern. This pattern is essential for the removal of interstitial fluid and the transportation of immune cells.

**Why the Correct Answer is Right**
The correct answer is related to the **deep inguinal lymph nodes**, which are responsible for draining the glans penis. This is because the lymphatic vessels of the glans penis converge to form larger lymphatic trunks that ultimately drain into the deep inguinal lymph nodes. The **spongy urethra** and **glans penis** share a common lymphatic drainage pathway.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the superficial inguinal lymph nodes primarily drain the skin of the penis and scrotum, not the glans penis.
**Option B:** This option is incorrect because the para-aortic lymph nodes are involved in the lymphatic drainage of the testes, not the glans penis.
**Option C:** This option is incorrect because the pelvic lymph nodes are involved in the lymphatic drainage of the prostate and other pelvic organs, not the glans penis.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the lymphatic drainage of the glans penis is primarily to the **deep inguinal lymph nodes**, which can be a site for metastasis in penile cancer.

**Correct Answer:** D. deep inguinal lymph nodes.