Anatomy of the male urogenital triangle

The diamond shaped perineum is divided into two triangles, the urogential triangle anteriorly and the anal triangle posteriorly. The urogenital triangle differs between males and females. In males, it contains male external genitalia and the perineal muscles. Let’s start with the male external genitalia, which includes the membranous - or intermediate - urethra, the spongy urethra, the scrotum, and the penis.

The membranous urethra begins at the inferior surface of the prostate gland, called the apex, then it passes through the deep perineal pouch, which houses the deep perineal muscles: the deep transverse perineal muscles and the external urethral sphincter. The deep transverse perineal muscle extends from the medial surface of the ischium to the perineal body. The external urethral sphincter is a circular muscle that surrounds the membranous part of the urethra and compresses it to maintain urinary continence. The deep perineal muscles are innervated by the deep branch of the perineal nerve.

Now, in the deep perineal pouch, posterolateral to the membranous urethra are a pair of pea-shaped glands called the bulbourethral or Cowper glands. The ducts of these glands cross the deep perineal pouch with the membranous urethra, and terminate by emptying into the proximal part of the spongy urethra. During sexual arousal, these glands secrete mucus-like secretion into the urethra.

Finally, the membranous part of the urethra extends through the bulb of the penis where it’s continuous with the last part of the urethra, called the spongy urethra. The spongy urethra is located within the corpus spongiosum and extends through the penis to the external urethral orifice. The spongy urethra contains an expansion in the glans penis called the navicular fossa.

Now, let’s discuss the scrotum, which is a fibromuscular sac that lies posteroinferior to the penis, and inferior to the pubic symphysis. The scrotum contains the testes and associated structures.