The Penis

The penis is formed of three tubular erectile tissues.  Two such tissues, the corpora cavernosa lie dorsally, with the third, the corpus spongiosum lying ventrally.  A section through the shaft of the penis is shown at right. The urethra enters the corpus spongiosum at the bulb and is enclosed by the erectile tissue of the corpus spongiosum along the shaft of the penis to the glans where it opens at the meatus (see image below).  Blood supply is by branches of the internal pudendal artery.  Deep arteries of the penis supply the corpora cavernosa, the artery of the bulb supplies the corpus spongiosum and paired dorsal arteries of the penis supply the rest of the structure.  Veins drain superficially into the internal pudendal veins, and to the prostatic plexus via the deep dorsal vein of the penis.  Nerve supply is from the pudendal nerve and pelvic autonomic plexuses.

The perineum

The perineal membrane fills in the triangle below the pubic arch.  The urethra passes through it from the prostate, forming the membranous urethra, and then into the corpus spongiosum as the bulbar urethra.  The erectile tissues of the corpori cavernosa and the corpus spongiosum lie on the perineal membrane.  Each of the erectile tissues is covered superficially by a thgin later of muscle - the ischiocavernosus and bulbospongiosus muscles.

Injury to the urethra within the perineum will allow urine to leak into a space which extends up the anterior abdominal wall, deep to the superficial fascia, but does not extend into the legs.

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