This is the perineal area and ventral abdomen of a male sea lion. Males have only one natural body opening below the tail (the ANUS), and a second natural opening into the PREPUCE, the PREPEUTIAL OPENING, located on the ventral abdomen, about 1/2 way between the anus and the UMBILICUS, or "belly button". The prepeutial opening can be seen in the center of this photograph. For sea lions, the umbilical scar is a small flat area of slightly depressed, hairless, dark-pigmented skin located near the base of the ribs (it is at the top center of this photograph).

In this photograph the PREPEUTIAL OPENING can be clearly seen as a depressed area of wrinkled and hairless skin in the center of the ventral abdomen.

Here the prosector is lifting the edges of the PREPUCE, showing the pink, nonpigmented skin that lies just inside the PREPEUTIAL OPENING.

Here the skin of the ventral abdomen has been removed to reveal the tip of the PENIS (on the magnification scale) and the TESTICLES (directly below the penis).

Note that the testicles are relatively small in relation to body size and are located just beneath the skin in the ventral pelvic region. Here the penis is still covered with a protective layer of skin called the PREPEUTIAL FOLD.

A closer view with the PREPEUTIAL FOLD SKIN pushed down to reveal the tip of the penis. In mature male sea lions, the core of the penis is formed from a specialized bone, called the OS PENIS or BACULUM that forms the rigid support structure of the penis. All marine mammals have an os penis. A small longitudinal groove is present along the ventral edge of the os penis to serve as a protective conduit for the fragile URETHRA.

A higher magnification view of the PENIS. The dark pink skin at the base of the penis is the PREPEUTIAL FOLD.

In this photograph the skin and subcutaneous tissues have been trimmed away to reveal the entire PENIS back to the point where it exits from the pelvic canal and the TESTICULAR TUNICS, specialized sacs containing and protecting the testes.

For normal sea lions, the testicular tunics are thin and transparent, so the testicles should be visible through the wall of the tunics, as shown here.

Because these sacs are connected to the abdomenal cavity through through small canals called the INGUINAL RINGS, opacity of the tunic wall or accumulation of fluid in these sacs could indicate a problem in the ABDOMENAL CAVITY.

In this photograph the penis has been deflected to one side and the abdominal cavity opened to show the spatial relationship between the BLADDER and EXTERNAL REPRODUCTIVE ORGANS, THE PENIS and TESTICLES.

Here the TESTICULAR TUNICS have been opened to reveal both TESTICLES. The long, dark structures connecting the tan-white testicles to the ventral body wall contain the VAS DEFERENTIA (singular is VAS DEFERENS), specialized tubes that carry mature sperm to the PROSTATE during ejaculation, and the PAMPINIFORM PLEXUS. The pampiniform plexus is a complex network of intertwined arteries and veins that 1.) SUPPLY BLOOD to the testicle and epididymus and 2.) HELP REGULATE the TEMPERATURE of the testicles several degrees below core body temperature to optimize production of spermatozoa (sperm cells). The vas deferens and pampiniform plexus pass through the ventral body wall into the pelvic cavity by traveling through specialized canals called INGUINAL RINGS. In humans, a painful inguinal HERNIA results from the traumatic passage of intestine or other structures into or through through the inguinal rings, and sometimes into the testicular tunic.

A higher magnification view of the TESTICLE (T) where SPERMATOZOA or SPERM are formed, the EPIDIDYMUS (E) where sperm are stored, the VAS DEFERENS (V) which conducts sperm to the PROSTATE (not shown), located near the base of the bladder, during ejaculation, the PAMPINIFORM PLEXUS (P), which supplies oxygenated blood to the testes and helps regulate testicular temperature, and the CREMASTER MUSCLE (C), a specialized muscle that lengthens and contracts to aid in testicular temperature regulation.

Another close-up view of these same structures.