The penis is composed of three main compartments: the paired corpora cavernosa and the corpus spongiosum. The tunica albuginea and the corpus spongiosum albuginea form the walls of the three compartments. The urethra lies within the corpus spongiosum.
The corpora cavernosa make up the bulk of the penis and consists of bundles of smooth muscle fibres intertwined in extracellular matrix. Within this compartment is a complex network of sinuses, arteries and nerve terminals.
The skin over the penis is highly flexible, allowing it to expand for an erection. At the distal end of the penis, the skin is attached to the corona of the glans and reflects forward to form the prepuce.