The inside of the scrotum is more complex than most people expect. Rather than a simple empty pouch holding two testicles, it contains multiple layers of tissue, a network of tubes, blood vessels, muscles, and protective fluid-filled membranes, all organized in a surprisingly intricate arrangement.
Layers of the Scrotal Wall
The scrotum itself isn’t just skin. Beneath the outer skin lies a thin layer of smooth muscle called the dartos, which is what gives the scrotal surface its wrinkled, ridged texture. This muscle contracts and relaxes constantly, pulling the testicles closer to the body in cold temperatures and letting them hang lower when it’s warm. That ongoing movement is a built-in cooling system: sperm production requires a temperature a few degrees below core body temperature, and the dartos muscle fine-tunes that positioning throughout the day.
Deeper still, a second muscle called the cremaster wraps around each testicle like a mesh. It’s a skeletal muscle, meaning it can contract quickly in response to touch, cold, or a sudden startle. Together, the dartos and cremaster give the scrotum its characteristic ability to visibly change shape and size from one moment to the next.
A vertical wall of tissue called the scrotal septum divides the inside into two separate compartments, one for each testicle. The two sides don’t communicate with each other internally, which is why a problem affecting one testicle (like an infection or swelling) doesn’t automatically spread to the other.
The Protective Membranes
Each testicle sits inside its own double-layered sac called the tunica vaginalis. Think of it like a balloon partially pushed in on itself: one layer (the visceral layer) clings directly to the surface of the testicle, and the other (the parietal layer) lines the inside of the scrotal compartment. Between these two layers is a thin film of clear, lubricating fluid.
That fluid allows the testicle to slide and rotate freely inside the scrotum, which helps it dodge impacts and pressure. Under normal circumstances, the tunica vaginalis wall is thin and transparent with a slight sheen, and the tissues beneath it are visible through it. The color ranges from pale orange-red to whitish, depending on the person.
What the Testicle Looks Like Inside
Each testicle is wrapped in a tough, white, fibrous capsule called the tunica albuginea. If you were to cut through it, you’d see that this capsule sends thin walls of tissue inward, dividing the interior of the testicle into roughly 250 small compartments called lobules. It looks somewhat like the inside of an orange, with wedge-shaped sections radiating from the center.
Each lobule contains one to four tightly coiled tubes called seminiferous tubules. These are where sperm are actually produced. Despite being packed into an organ the size of a small plum, the tubules are extraordinarily long when uncoiled. Between the tubules sit clusters of specialized cells that produce testosterone and release it directly into the bloodstream.
In terms of overall size, an adult testicle typically measures around 10 to 11 milliliters in volume, roughly the size of a large olive or small walnut. It’s normal for one testicle to be slightly larger than the other or to hang a bit lower.
The Epididymis and Connecting Tubes
Sitting along the back and top of each testicle is a long, tightly coiled tube called the epididymis. It has three sections: a head at the top of the testicle, a body running along the back, and a tail at the bottom. If you’ve ever felt a soft, ridge-like structure behind a testicle, that’s the epididymis.
Sperm produced inside the testicle travel into the epididymis, where they spend several weeks maturing and gaining the ability to swim. The tail of the epididymis connects to the vas deferens, a firm, muscular tube about the diameter of a piece of spaghetti. The vas deferens runs upward through the spermatic cord, exits the scrotum through the inguinal canal, and eventually reaches the urethra. It’s the tube that gets cut during a vasectomy.
Blood Vessels and the Spermatic Cord
Each testicle hangs from a spermatic cord, which is the rope-like structure you can feel running from the top of the testicle up toward the groin. Inside each cord is a bundle of arteries, veins, nerves, the vas deferens, and the cremaster muscle, all wrapped together in connective tissue.
The veins in the spermatic cord form a tangled network called the pampiniform plexus. This web of small veins wraps around the artery supplying blood to the testicle, and it serves a clever purpose: warm arterial blood flowing down toward the testicle transfers heat to the cooler venous blood flowing back up, pre-cooling the blood before it reaches the testicle. It’s essentially a built-in heat exchanger. The right and left venous systems are independent, with no crossover connections between the two sides in the scrotum or pelvis.
How Common Conditions Change the Interior
Two of the most common conditions visibly alter the internal appearance of the scrotum. A hydrocele occurs when excess fluid accumulates in the space between the two layers of the tunica vaginalis, turning what’s normally a thin film of lubricant into a noticeable fluid-filled sac around the testicle. It makes the affected side of the scrotum swell and feel heavy, though it’s typically painless.
A varicocele is an enlargement of the veins in the pampiniform plexus, essentially varicose veins inside the spermatic cord. In mild cases, the enlarged veins are only detectable on ultrasound. In more advanced cases, the swollen veins can be felt as a soft mass above the testicle. Large varicoceles are often described as feeling like a bag of worms. They occur on the left side in about 80 to 90 percent of cases, because of differences in how the left and right testicular veins drain. Varicoceles are one of the most common correctable causes of reduced sperm production.