First

In humans, the outside of the foreskin is like the skin on the shaft of the penis but the inner foreskin is a mucous membrane like the inside of the eyelid or the mouth. Like the eyelid, the foreskin is free to move. Smooth muscle fibres keep it close to the glans but make it highly elastic.[2] The foreskin is attached to the glans with a frenulum which helps retract the foreskin over the glans. At the end of foreskin there is a band of tissue called the ridged band which, according to one study, is rich in nerve endings called Meissner's corpuscles.[3] According to a NOCIRC-funded study by Sorrells et al., the five most sensitive areas of the penis are on the foreskin.[4]
In children, the foreskin covers the glans completely but in adults this need not be so. Schöberlein [5] found that about 50% of young men had full coverage of the glans, 42% had partial coverage, and in the remaining 8%, the glans was uncovered. After adjusting for circumcision, he stated that in 4% of the young men the foreskin had spontaneously atrophied (shrunk).