Your dog almost certainly doesn’t have four testicles. What you’re seeing are two normal testicles plus two bulb-shaped structures at the base of the penis called the bulbus glandis. These rounded bumps sit just in front of the scrotum and can swell to a surprisingly large size, making it look like your dog has an extra pair. It’s one of the most common anatomical mix-ups among dog owners.
What the Bulbus Glandis Actually Is
The bulbus glandis is a pair of erectile tissue structures located on either side of the base of your dog’s penis. When your dog becomes aroused or excited (not necessarily in a sexual way), these structures fill with blood and create two firm, visible bumps beneath the skin. They can look alarmingly like testicles, especially if you’ve never noticed them before.
This swelling is completely normal. It can last anywhere from a few minutes to about an hour, and as long as it goes back down and your dog seems comfortable, there’s nothing to worry about. You might notice it more during play, when greeting other dogs, or seemingly at random. The bulbus glandis exists in all intact and neutered male dogs, though it tends to be more noticeable in short-haired breeds where the skin is thinner.
How to Tell Testicles From the Bulbus Glandis
Location is the easiest way to distinguish them. Your dog’s two testicles sit inside the scrotum, which hangs between the hind legs. The bulbus glandis sits further forward, at the base of the penis closer to the belly. If you’re seeing two lumps behind the penis and two lumps in front of it, you’re looking at two different anatomical structures doing two different jobs.
The feel is different too. Testicles are oval, smooth, and relatively firm but movable inside the scrotal sac. The bulbus glandis, when swollen, feels rounder and firmer, almost like a marble under the skin. When not engorged, it may be barely noticeable at all, which is why many owners are startled the first time they see it swollen.
Could a Dog Actually Have Four Testicles?
Technically, yes, but it’s extraordinarily rare. The condition is called polyorchidism, and as of the most recent veterinary literature, it has been documented in only a single published case in dogs. In humans, slightly over 100 cases have ever been reported. Diagnosing it requires ultrasound imaging and histological confirmation, meaning a vet would need to examine tissue samples under a microscope to verify the extra testicle is real testicular tissue and not something else.
In the one documented canine case, the extra testicle was found inside the abdomen, not in the scrotum. It was discovered during an ultrasound as an oval structure about 2.2 cm long sitting near the bladder. So even in the rare event a dog does have a supernumerary testicle, you probably wouldn’t see it from the outside.
Other Lumps That Can Mimic Extra Testicles
If what you’re feeling doesn’t match the bulbus glandis description, a few other possibilities are worth knowing about.
Inguinal or scrotal hernias occur when abdominal contents push through the inguinal canal into the groin or scrotum. They create swelling that can look like an extra mass near the testicles. In dogs, these hernias sometimes cause vomiting or discomfort, especially if intestinal tissue gets trapped. The swelling is often asymmetrical, appearing larger on one side.
Swollen lymph nodes in the groin area can also feel like unexpected lumps. Male dogs have a cluster of one to three superficial inguinal lymph nodes on each side, sitting in the fatty tissue near the base of the penis. They’re normally small, but when inflamed or affected by disease, they can grow quite large, up to several centimeters. Swollen lymph nodes in this area can signal infection, inflammation, or in some cases metastatic cancer.
Testicular tumors are another possibility, particularly in older intact males. Dogs develop three main types of testicular cancer. A tumor can make one testicle noticeably larger or harder than the other, or you might feel a distinct mass inside. Some testicular tumors produce hormones that cause secondary changes like hair loss on the trunk, darkened skin, or enlarged mammary tissue. Dogs with an undescended testicle (cryptorchidism) are at higher risk for certain tumor types, though those tumors wouldn’t be visible externally since the retained testicle sits inside the body.
When the Lumps Need a Closer Look
If your dog’s “extra” lumps are at the base of the penis, change size with arousal, and resolve within an hour, you’re almost certainly looking at a normal bulbus glandis. No action needed.
The picture changes if you notice lumps that are persistently swollen, growing over time, hard or irregular in texture, painful to the touch, or accompanied by other symptoms like vomiting, lethargy, or changes in your dog’s coat. A vet can distinguish between normal anatomy and a problem using a simple physical exam. If there’s any uncertainty, ultrasound is the standard next step. It’s fast, non-invasive, and highly accurate at differentiating tumors from normal tissue. More advanced techniques like contrast-enhanced ultrasound can detect both cancerous and non-cancerous testicular lesions with roughly 87% sensitivity and 100% specificity.
For most dogs, though, the answer is simple: those aren’t four testicles. They’re two testicles and two perfectly normal bulbs of erectile tissue doing exactly what they’re supposed to do.