Is there one?
And while I’m on the subject, why do all the common words for that type of “structure” starts with a ‘c’? Crack, crevice, crease, canyon, chasm. Are there non-‘c’ words that I just can’t think of?
Gluteal cleft.
And yes, there is one other c-word you’re forgetting, but let’s forget it.
Cleavage?
fissure, rift, rima, rimation, rime, split RAVINE, arroyo, , gap, gorge, gulch , split
Plumbers Crack. This is from CAP;
I had to look it up.
Damn! PapaBear, you beat me to it1
Zymurgist
Abandoning all hope of finding the medically/physiologically appropriate term (or, taking Nickrz’ post as definitive), I’ll post my contributions toward finding a usefull popular term.
That was my first thought, but it somehow needs a modifier to keep us able to distinguish between the top end of a north bound female and the bottom end of a (pear-shaped, usually) south bound male.
I don’t have a punchline - I’m just jamming.
Southside cleavage?
Butt cleavage?
Cleavage best left unseen?
“Pull up your pants!” cleavage?
Uh Nickrz? Close, but they are actually two different areas. Let’s hope you remember this the next time your with a woman. 
>^,^<
KITTEN
Coarse and violent nudity. Occasional language.
Hey, he said “structure” and there tain’t much between them!
I can think of another c-word, but I’ll keep it to myself 
I recall hearing the term Anal Cleft used in a discussion of whats acceptable of TV, back when the thong bikini was just becoming mainstream. It was used on a variety of networks, and in reference to some obsenity laws violated by those bikini hot dog vendors in New York and Miami.
Gleutal Cleft seems more accurate, but for some reason they used Anal Cleft. I’m certain that theres a medical name for it, you wouldn’t believe the body parts and regions they’ve named. They even name the areas that don’t have things there, like the space between your fingers.
What about the indentation between the nose and upper lip? Always wondered…
Snot chute?
Actually, if I’m reading my Gray’s Anatomy correctly that would be the “dilatator naris posterior”.
I told my kids the name for “butt crack” is vertical smile they loved it!
I thought it was called the “Loverock”. Huh huh huh.
“Owls will deafen us with their incessant hooting!” W. Smithers
Filtrum or philtrum; I’ve seen it spelled both ways.
I taught my son filtrum when he was a wee lad (at five he’s now a big boy). He uses the word as one would use “nose” or “chin”. It’s really quite cute.
As for the butt-crack, how about posterior rugae. I have this wonderful book titled The Macmillan Visual Dictionary It’s full of pictures with labels. It spells filtrum as philtrum.
Cheers,
-Sweet,E
And while we’re at it, how about that area between the bottom of the vagina and the anus? I know the official term is “perineum,” but “chin rest” always seemed more appropriate to me.
;^P
Live a Lush Life
Da Chef
Cross that fine line and (trust me) it is quite noticable.
>^,^<
KITTEN
Coarse and violent nudity. Occasional language.
I could get crude and ask “in which direction am I to travel?” but such things are beneath me.