A meatus is an opening; therefor, it's a depression, not a projection.
projection
projection
projection
projection
is a depression
....opening?
A fissure is an opening or crack in the Earth's crust, typically where tectonic plates meet. It is not a projection or depression, but rather a narrow, long fracture in the ground.
"A crest is a projection or ridge, especially of bone; cresta"source: chacha.com
projection. The bumps of bone around your knees and elbows are almost all called condyles.
The term for the small conical projections along the wall of the renal sinus of a kidney is "renal papilla."
of Sinus, An opening; a hollow; a bending., A bay of the sea; a recess in the shore., A cavity; a depression., A cavity in a bone or other part, either closed or with a narrow opening., A dilated vessel or canal., A narrow, elongated cavity, in which pus is collected; an elongated abscess with only a small orifice., A depression between adjoining lobes.