projection
Depression
fissure
A fissure
A volcanic vent or fissure (depending on the type of eruption).
A fissure can mean a split in the geological structure of the earth or any opening in the body. A foramen is an opening that can connect the bodily systems together. Foramen does not pertain to geological structures but just biological things. See related links below for more information and sources
The human brain has a transverse fissure. The fissure is a deep line that separates the cerebrum from the cerebellum.
....opening?
is a depression
A meatus is an opening; therefor, it's a depression, not a projection.
projection
projection
projection
projection
A rounded opeing through a bone is called a foramen.
"A crest is a projection or ridge, especially of bone; cresta"source: chacha.com
fissure
A sulcus is a depression or fissure in the surface of the brain.
A fissure