In some animals the male

penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males d ...

possesses a

muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of mus ...

enabling retraction into the prepuce.

In particular animals

The retractor penis muscle occurs in marsupials and

carnivoran Carnivora is a monophyletic order of placental mammals consisting of the most recent common ancestor of all cat-like and dog-like animals, and all descendants of that ancestor. Members of this group are formally referred to as carnivorans, ...

s, 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. In Tandonia, the retractor penis inserts at the boundary between the penis and epiphallus.

"Genus summary for ''Tandonia''"

AnimalBase AnimalBase is a project brought to life in 2004 and is maintained by the University of Göttingen, Germany. The goal of the AnimalBase project is to digitize early zoological literature, provide copyright-free open access to zoological works, and pr ...

, last modified 23 May 2010, accessed 26 August 2010. In stallions, the retractor penis muscle is relatively underdeveloped. The retractor muscle contracts to retract the penis into the sheath and relaxes to allow the penis to extend from the sheath. In bulls, protrusion is not affected much by erection, but more by relaxation of the retractor penis muscle and straightening of the sigmoid flexure.

References

{{reflist Penis Muscular system