That extra pair of round lumps you’re seeing near your dog’s penis is almost certainly the bulbus glandis, a completely normal part of canine anatomy. Every intact male dog has one, and when it swells, it creates two distinct bulges just in front of the scrotum that can look startlingly like a second set of testicles.
What the Bulbus Glandis Actually Is
Your dog’s penis has a structure that most other mammals don’t: a bulb-shaped section of erectile tissue near its base called the bulbus glandis. This tissue sits inside the prepuce (the sheath of skin covering the penis) and wraps around the base of the penile bone. When it fills with blood, it expands to two or three times the diameter of the penile shaft, forming two rounded lobes that push outward and become visible through the skin.
Because these two lobes sit just ahead of the scrotum, the visual effect is unmistakable. You see two lumps in front (the swollen bulbus glandis) and two lumps behind (the actual testicles), creating the “four testicle” appearance. The bulbus glandis serves a reproductive purpose: during mating, it swells dramatically and locks the male and female together in what breeders call a “tie.” But mating isn’t the only thing that triggers it.
Why It Swells When Your Dog Isn’t Mating
Sexual arousal is the most obvious trigger, but the bulbus glandis can swell from any form of excitement. A trip to the dog park, meeting a new dog, getting worked up during play, or even rolling around on their back can cause enough stimulation for the tissue to engorge temporarily. Some dogs show this more prominently than others depending on their size, body composition, and how much skin covers the area.
The swelling typically goes down on its own within minutes once your dog calms down. If you notice the bulges appear and disappear with your dog’s activity level, that’s a reliable sign you’re looking at normal anatomy doing normal things. Persistent swelling that doesn’t resolve, or any sign of pain when the area is touched, is not normal and warrants a closer look from your vet.
How to Tell the Difference From Actual Testicles
Location is the easiest way to distinguish the two. The scrotum sits between your dog’s hind legs, further back toward the tail. The bulbus glandis sits further forward, closer to the belly, just in front of where the penile sheath meets the abdomen. If you gently feel the area (when your dog is calm and the swelling has gone down), you’ll notice the front lumps are part of the penile sheath and feel softer, while the testicles in the scrotum feel firmer and more distinct, each contained in its own compartment.
The timing also tells the story. Testicles are always present and roughly the same size. The bulbus glandis changes dramatically, sometimes flat and invisible, other times round and prominent. If the “extra testicles” come and go, they’re not testicles.
Other Causes of Lumps in the Groin Area
While the bulbus glandis explains the vast majority of “four testicle” sightings, a few other conditions can produce lumps in this region that are worth knowing about.
Inguinal Hernias
An inguinal hernia occurs when fat, intestine, or other abdominal contents push through a weak spot in the muscle wall near the groin. The first sign is usually swelling in the groin area. An uncomplicated hernia feels soft and can often be gently pushed back into place without causing pain. A complicated hernia, where tissue becomes trapped, creates firm swelling that can’t be pushed back and is often painful, with the skin sometimes appearing bruised or reddened. Vomiting, difficulty urinating, or lethargy alongside groin swelling are signs of a complicated hernia that needs prompt veterinary attention.
Retained Testicles
Most puppies have both testicles fully descended into the scrotum by 2 months of age, though some take up to 6 months. A retained testicle (cryptorchidism) can sometimes lodge in the inguinal canal, the passageway between the abdomen and the groin, where it creates a palpable lump under the skin. If your dog has only one testicle visible in the scrotum and you’re seeing an extra lump in the groin, a retained testicle is a real possibility. Retained testicles carry a higher risk of developing tumors and are typically removed surgically.
Testicular Tumors
In intact adult dogs, testicular tumors can cause one or both testicles to enlarge, creating an asymmetric or unusually bulky appearance. Warning signs include soft swelling in one or both testicles, one testicle noticeably larger than the other, and generalized scrotal enlargement. Some testicular tumors produce hormones that cause secondary changes elsewhere on the body: symmetrical hair loss, brittle coat, thin skin, darkening of the skin, or a stripe of red inflammation running along the midline of the penile sheath. These skin changes are particularly distinctive and should prompt a vet visit.
Swollen Lymph Nodes or Fat Pads
Dogs have superficial inguinal lymph nodes located near the groin, between the inner thigh and the lower abdomen. When these swell due to infection or, less commonly, cancer spreading through the lymphatic system, they can create visible lumps. Normal inguinal fat pads, which are simply pockets of fat in the groin region, can also become more prominent in overweight dogs and mimic the appearance of abnormal swelling.
What to Look For Going Forward
If the lumps you’re seeing appear during excitement and resolve within a few minutes, you’re looking at the bulbus glandis and everything is fine. Keep an eye out for a few things that would change that assessment: swelling that stays for hours or doesn’t go down at all, any sign of pain or tenderness when your dog sits or when the area is touched, changes in skin color like bruising or darkening, asymmetry between the two actual testicles, or any new lump that feels firm and immovable. Hair loss or skin changes around the groin and belly, especially if they appear symmetrically on both sides of the body, can signal a hormone-producing tumor.
For puppies under 6 months, it’s worth having your vet confirm that both testicles have descended into the scrotum at a routine checkup. If only one is present by 4 months, your vet will likely begin monitoring for cryptorchidism.