Anatomy
The
penis has two major internal divisions, each responsible for a different function.
The corpora cavernosa, which can be likened to hydraulic cylinders, create
structural rigidity. The corpus spongiosum contains the urethra, or excretory
channel.
The corpora cavernosa are cigar-shaped tubes of strong connective tissue, filled with spongy muscle-lined cavities. Relaxation of vascular muscle causes inflow of blood and expansion of the corpora’s inner sponge during erection. As a result its wall, the tunica albuginea, is stretched tightly enough to produce rigidity. In addition to defining the shape of the erect penis, the tunica also has a key role in limiting blood outflow during erection.
The
paired corpora are joined within the penis, but separate at its junction with
the body. At its base they diverge right and left, and attach to the corresponding
pelvic bones. These two points, along with a midline suspensory ligament between
the joined corpora and the pubic bone, form a sturdy three-point anchor.
The urinary channel or urethra runs under the corpora cavernosa, while most of the penile blood vessels and nerves run along the top side.
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