I don't mean to sound banal, but aren't there enough women doing anal? I know the many medical risks are quite trite, so I shall instead focus on appearance tonight. That of the anus is not quite famous. Even so, people have actually studied this part, although they may not have considered it worthy of art. If one ponders and considers the browneye for years yonder, then you might thither realize the truth about this necessary wonder.

So, without further ado, here is where I shall cover this topic for you:

"The anus is a longitudinal slit-like aperture which becomes oval during defecation. It is situated an equal distance from the tuberosities of the ischii and about one inch anterior to the tip of the coccyx. It is a little more anterior in the female than in the male... The skin surrounding the anal orifice is arrayed in radiating folds, the result of contraction of the corrugator cutis ani muscle."
http://www.intestinaldisorders.net/anatomy-anus-and-rectum.html

"Anal fissures, rhagadia ('tears'), hemorrhoids, the obliteration of the radial folds around the anus, and a loosening of the anus itself could all indicate signs of penetration, although Zacchia did warn that such conditions could be caused by other means (such as constipation). Even if it was outside their area of expertise, Zacchia stated, 'doctors can easily pronounce the truth concerning this matter' (Rousseau, 2008: 82)."
http://www2.warwick.ac.uk/fac/soc/sociology/rsw/undergrad/cetl/ejournal/issues/volume1issue2/brooks

"Another, so to say, classical sign of [anal intercourse], is the obliteration around the anus of the radial skin-folds"
http://www.archive.org/details/sexualinstinctit00tarnuoft