**Core Concept**
The bulbourethral glands, also known as Cowper's glands, are a pair of small exocrine glands located in the deep perineal pouch of the male pelvis. They play a crucial role in the male reproductive system by secreting a clear, alkaline fluid that helps to neutralize acidic semen and lubricate the urethra.

**Why the Correct Answer is Right**
The bulbourethral glands secrete their fluid into the membranous urethra, which is a short, muscular segment of the urethra that passes through the urogenital diaphragm. This fluid helps to prepare the urethra for ejaculation by reducing its pH and increasing its lubrication. The membranous urethra is a critical structure in the male urethra, as it is the narrowest part and most susceptible to injury during urological procedures.

**Why Each Wrong Option is Incorrect**
* **Option A:** The bulbourethral glands do not open into the prostatic urethra, which is the longer, more proximal segment of the male urethra that passes through the prostate gland. The prostatic urethra is lined with prostatic glands and is not directly involved in the secretion of the bulbourethral glands.
* **Option B:** The bulbourethral glands do not open into the penile or spongy urethra, which is the long, thin segment of the male urethra that passes through the corpus spongiosum of the penis. While the penile urethra is the primary site of semen ejaculation, it is not directly connected to the bulbourethral glands.

**Clinical Pearl / High-Yield Fact**
The bulbourethral glands are an important consideration in urological procedures, such as transurethral resection of the prostate (TURP), where the membranous urethra is at risk of injury. Understanding the anatomy of the male urethra and the role of the bulbourethral glands is crucial for safe and effective surgical interventions.

**Correct Answer:** C. Membranous urethra