**Core Concept**
In the female lower genitourinary tract, there are specific sphincters that control the flow of urine and maintain continence. These sphincters are essential for understanding the anatomy of the female urethra and its surrounding structures.

**Why the Correct Answer is Right**
The internal urethral sphincter is a non-existent structure in females. In males, the internal urethral sphincter is a ring-like muscle that surrounds the membranous part of the urethra and plays a key role in controlling the flow of urine. However, in females, the urethra is surrounded by the pubovaginalis muscle, which provides support to the pelvic floor and contributes to urinary continence. The external urethral sphincter, on the other hand, is present in both males and females and is responsible for voluntary control over urination.

**Why Each Wrong Option is Incorrect**
**Option A:** Pubovaginalis is indeed a sphincter of the lower genitourinary tract in females, providing support to the pelvic floor and contributing to urinary continence.
**Option B:** External urethral sphincter is a correct sphincter of the lower genitourinary tract in females, responsible for voluntary control over urination.
**Option D:** Bulbospongiosus is a muscle of the perineum that surrounds the bulb of the vestibule in females, but it is not a sphincter of the lower genitourinary tract.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the female urethra is shorter and more mobile than the male urethra, and the pubovaginalis muscle plays a crucial role in maintaining urinary continence in females.

**✓ Correct Answer: C. Internal urethral sphincter**