The anatomically intact male. His penis is flaccid and his glans is covered, as usual, by his foreskin.
The gradual retraction of the foreskin, from total coverage (top left) to full retraction upon erection (bottom right).
An intact penis upon erection. Though the foreskin retracts behind the glans during erection, there is still a lot of skin available on the penis, allowing the foreskin to glide up and back down over the glans. The intact model in the photo is demonstrating this by rolling the foreskin up onto the glans. This is the action generating the primary erogenous response in intact males. It is, sadly, not possible after circumcision.
The intact penis with foreskin retracted. Notice the sensitive, shiny, moist quality of the glans, which is so because it has been protected by the foreskin from contact with outside elements. The foreskin is made up of almost all the skin visible on the shaft of the penis, which when returned over the glans will cover it wholly. The average foreskin comprises 12.5cm x 9cm (5" x 3") of tissue.
Comparison with the Circumcised Penis
The penis on the left is intact, like those above. The penis on the right has been circumcised some time ago. Notice how the glans is unprotected and has dried out and hardened ("keratinised") due to constant contact with external abrasion.
Another circumcised penis. The glans, once again, is dried out and bears signs of keratinisation. The circumcision scar is plainly visible beneath the glans around the entire shaft. There is little skin available for expansion of the penis to occur upon erection, and will therefore become very tight once erect