Normal Anatomy of the Penis

From Within:

The penis is composed of three cylinders enclosed in 2 thin layers of muscle/fascia and a layer of skin. The tip carries the glans, a bell shaped mass of erectile tissue that is very sensitive to touch as it is rich in nerve endings.

One of the three cylinders is the corpus spongiosum that contains the urethra. The urethra is the tube through which urine flows. It ends in the glans with the urethral meatus (opening through which urine flows. The corpus spongiosum courses along the length of the penis, on its under surface, under the skin.

The two other cylinders are the corpora cavernosa. These are the structures responsible for rigidity and therefore erection. The course next to each other above the corpus spongiosum under the skin of the upper surface of the penis. Each corpus cavernosum is composed of erectile tissues in the form of microscopic spherical spaces (Sinusoids) that accommodate blood and expand when blood flow into them increases. Each sinusoid is surrounded by microscopic muscles that control its diameter. The sinusoids are enclosed in the outer wall of the corpus cavernosum that is a firm, expandable layer of fibrous tissue named the "tunica albuginea".

The neurovascular bundle is a collection of nerves, arteries and a vein that course along the penis on its upper surface, from the glans to the base of the penis. It includes the nerves that convey sensation from the glans: the dorsal nerve of the penis.

 

 

At the base of the penis (towards the abdomen), the corpora cavernosa are attached to the bony pelvis by adhesions to between their deepest parts (the crura) and bone, and by a ligament that attaches the corpora cavernosa to the middle of the pelvis and to the anterior abdominal wall: the suspensory ligament.

 

Each corpus cavernosum has a feeding artery that fills it with blood, and a draining vein that lets blood out. The vein starts inside the corpus cavernosum between its wall (tunica albuginea) and the sinusoids, such that if the sinusoids expand, they may compress the vein and prevent blood from exiting the corpus cavernosum.

The penis is covered by skin, underneath which is a thin layer of tissue named the Colle's fascia, beneath which is a thin muscle called Dartos Muscle or Buck's fascia

 

From Without:
 

Length:

Normal length is variable from race to race, but there is an accepted average. Measurement are taken in the non-erect state by pulling on the glans forwards to stretch the penis and dipping the ruler into the pubic fat that surrounds the penis down to the bone, so that the measurement is taken from the bone to the glans, and not from the skin to the glans. This measures the actual length of the penis and not the apparent length. The stretched non-erect length should at least be 7cm. In the erect state, length measured in the same way should be at least 11 cm. The length of the vagina is 10cm on average, which makes 11 cm a normal length for the penis.

 Width / Diameter:

There is no consensus about the normal diameter, but if measured with a taper, the perimeter should at least be 10cm. It has to be noted that the vagina is surrounded by muscles that tighten it around the penis, regardless its diameter.

Straightness:

The penis is mostly straight. However, many men have variable degrees of curvature affecting the penis. This poses cosmetic problems. This may also make intercourse difficult or painful to the female if curvature is more than 30 degrees, especially it is downwards or to a side.

By curvature we mean that the penis is straight at its base but has a bending point distally. A straight penis pointing upwards, downwards or to a side without a bent is not considered curved.

Angle:

The penis usually makes an angle of around 90 degrees relative to the surface of the abdomen. This may vary. The angle may be acute with the penis pointing upwards, or obtuse with the penis pointing downwards. This is acceptable as long as it does not make intercourse difficult or disturb the individual or his partner psychologically. A rigid penis pointing downwards is an erect penis. Erection does not necessarily mean that the penis should point forwards or upwards.

Urethral Meatus:
This is the urine outlet at the tip of the penis in the glans. Hypospadias is a disorder where the urethral meatus is not at the tip but is somewhere along the lower surface of the penis. This may require surgical correction.