The penis has three parts: the root (hidden inside your body), the body (the shaft you can see), and the glans (the head). The root contains the crura — two "legs" of erectile tissue that diverge and anchor to your pelvic bones. This internal structure is not visible externally.
The penis is composed of three cylinders of spongy erectile tissue: two corpora cavernosa (the main chambers that fill with blood during erection) and one corpus spongiosum (which surrounds the urethra and forms the glans).
What most people don't realize is that the corpora cavernosa don't just start at the base of the visible shaft. They extend backward and split into two separate structures called the crura (singular: crus), which attach to the underside of the ischiopubic rami — part of your pelvic bone.
Simplified diagram — not to scale. Actual anatomy varies between individuals.
Located in the superficial perineal pouch of the pelvic floor, the root is not visible externally. It contains the two crura (anchoring the corpora cavernosa to the pelvic bone) and the bulb of the penis (an expansion of the corpus spongiosum). Two muscles — the ischiocavernosus and bulbospongiosus — surround these structures and contribute to erection rigidity and ejaculation.
The free-hanging part of the penis, suspended from the pubic symphysis by the suspensory ligament. It contains the three erectile cylinders running in parallel — two corpora cavernosa on top and one corpus spongiosum on the underside surrounding the urethra.
The distal expansion of the corpus spongiosum. It contains the opening of the urethra (external urethral orifice) and is richly supplied with nerve endings, making it the most sensitive part of the penis.
This isn't just anatomical trivia. Understanding the full structure of the penis has practical implications:
When men gain weight, the pubic fat pad can bury more of the external shaft, making it appear shorter. The penis isn't shrinking — more of it is just being hidden. This is also why "bone-pressed" measurements (pushing the ruler into the fat pad until it hits the pubic bone) are the standard in clinical research. You're measuring closer to the actual total external length.
The ischiocavernosus muscles that surround the crura actively contract during the rigid erection phase, forcing blood from the crura into the rest of the corpora cavernosa. Your erection isn't just passive blood-filling — there's an active muscular assist happening inside your body that you can't see.
The suspensory ligament connects the visible shaft to the pubic bone. Its length and tension determine your erection angle and how much of the shaft hangs externally. Some penile lengthening surgeries involve releasing this ligament — which doesn't actually make the penis longer, just allows more of the existing internal structure to hang outside the body (with trade-offs like reduced erection angle).
💡 The Takeaway: You're carrying more than you can see. The total erectile structure — from the tip of the glans to the ends of the crura — is significantly larger than the external measurement. This is normal anatomy that applies to every male body.
This is standard content in medical school anatomy courses. Gray's Anatomy (the textbook, not the show) has covered the crura and root of the penis since the 1800s. Britannica describes the crura as "projections" that attach to the edges of the pubic arch. TeachMeAnatomy, Kenhub, and every reputable anatomy reference describes the same three-part structure.
But high school health class? It's usually a side-view diagram with a label pointing to the urethra and a quick mention of the vas deferens. The internal root structure simply isn't covered, despite being one of the most interesting (and reassuring) pieces of male anatomy.
Some products and surgeries claim to "unlock" the hidden internal penis. Be skeptical. Suspensory ligament release surgery can technically expose more shaft, but it comes with real trade-offs — reduced erection angle, potential instability, and complications. The internal structure exists for a reason: it anchors and supports erections. Don't let anyone sell you surgery on the premise that you have "hidden length" waiting to be freed.
The visible portion is what clinical studies measure. See your percentile from the Veale 2015 dataset of 15,521 men.
Calculate Your Percentile →Your penis has a hidden root structure — the crura — that extends deep into your pelvis and anchors to the pubic bone. The external portion you see represents roughly two-thirds of the total structure. This is basic anatomy, documented in every medical textbook, and almost never taught outside of medical school.
It doesn't change your functional size or how things work in practice. But it's a genuinely interesting piece of body knowledge that tends to shift how guys think about their anatomy — usually for the better.