Failure of the retractor penis muscles to relax and to allow the penis to extend from the sheath is known as

Failure of the retractor penis muscles to relax and allow the penis to extend from the sheath is known as Impotentia coeundi.
The retractor penis muscle occurs in marsupials and carnivorans, but it is absent in humans. A stag's penis forms an S-shaped curve when it is not erect and is retracted into its preputial sheath by the retractor penis muscle.
Impotentia coeundi is characterized by normal sexual desire and normal ability to copulate but the fertility is either subnormal or absent.