**Core Concept**
The external urethral sphincter is a skeletal muscle that plays a crucial role in voluntary urine control. It is part of the urogenital diaphragm, which is a fascial layer that separates the deep perineal space from the superficial perineal space.

**Why the Correct Answer is Right**
The external urethral sphincter is located in the deep perineal space, which is a fascial compartment between the inferior fascia of the urogenital diaphragm and the superior fascia of the perineal membrane. This space contains the external urethral sphincter, the bulbospongiosus muscle, and the deep transverse perineal muscle. The external urethral sphincter surrounds the membranous part of the urethra, which is the part of the urethra that passes through the urogenital diaphragm.

**Why Each Wrong Option is Incorrect**
**Option A:** The ischiorectal fossa, also known as the ischioanal fossa, is a fat-filled space located lateral to the anal canal and is not directly related to the external urethral sphincter.
**Option B:** The extraperitoneal space refers to the space outside the peritoneal cavity, which is not relevant to the location of the external urethral sphincter.
**Option C:** The retropubic space is a fascial space located between the bladder and the pubic bone, which is not where the external urethral sphincter is located.

**Clinical Pearl / High-Yield Fact**
The external urethral sphincter is a critical muscle for maintaining urinary continence, and damage to this muscle can lead to urinary incontinence. Understanding the anatomy of the external urethral sphincter is essential for urologists and surgeons performing procedures related to the urethra and bladder.

**✓ Correct Answer: D. Deep perineal space**