**Core Concept**
The prostatic sinus is a venous plexus located within the prostate gland, playing a crucial role in the drainage of the gland. Understanding the anatomy of the prostatic sinus is essential for appreciating the pathophysiology of urinary retention and other prostate-related disorders.

**Why the Correct Answer is Right**
The correct answer refers to the prostatic urethra's opening into the prostatic sinus. This opening is facilitated by a longitudinal fold of mucous membrane, known as the **prostatic sinus ostium**. As the prostatic urethra passes through the prostate gland, it opens into the prostatic sinus, which is a venous plexus that surrounds the gland. This opening is significant in the context of prostate surgery and the management of urinary retention.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because the prostatic sinus is not directly related to the ejaculatory ducts.
**Option B:** Incorrect because the prostatic sinus is not directly related to the seminal colliculus.
**Option C:** Incorrect because the prostatic sinus is not directly related to the verumontanum.

**Clinical Pearl / High-Yield Fact**
The prostatic sinus ostium is a critical landmark in prostate surgery, as it marks the transition from the prostatic urethra to the prostatic sinus. This area is also relevant in the context of urinary retention, where the prostatic sinus can become obstructed, leading to urinary retention.

**Correct Answer:** D.