The urethal crest is an anatomical feature present in the urinary system

Urinary system

The urinary system is the organ system that produces, stores, and eliminates urine. In humans it includes two kidneys, two ureters, the bladder and the urethra.-Kidney:...

 of both males and females.

In males, the urethral crest is known as the crista urethralis masculinae, or the crista phallica,
and is a longitudinal fold on the posterior wall of the urethra

Urethra

In anatomy, the urethra is a tube that connects the urinary bladder to the genitals for the removal of fluids out of the body. In males, the urethra travels through the penis, and carries semen as well as urine...

 extending from the uvula of the bladder

Uvula of urinary bladder

The mucous membrane immediately behind the internal urethral orifice presents a slight elevation, the uvula of urinary bladder, caused by the middle lobe of the prostate....

 through the prostatic urethra

Prostatic urethra

The prostatic urethra, the widest and most dilatable part of the urethra canal, is about 3 cm. long.It runs almost vertically through the prostate from its base to its apex, lying nearer its anterior than its posterior surface; the form of the canal is spindle-shaped, being wider in the middle...

.
It is from 15 to 17 mm. in length, and about 3 mm. in height, and contains muscular and erectile tissue.
When distended, it may serve to prevent the passage of the semen

Semen

Semen is an organic fluid, also known as seminal fluid, that may contain spermatozoa. It is secreted by the gonads and other sexual organs of male or hermaphroditic animals and can fertilize female ova...

 backward into the bladder

Urinary bladder

The urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. A hollow muscular, and distensible organ, the bladder sits on the pelvic floor...

.

In females, it is known as the crista urethralis femininae, and is a conspicuous longitudinal fold of mucosa on the posterior wall of the urethra.