membrane bone

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A bone that forms directly in membranous connective tissue, as some cranial bones, instead of developing from cartilage.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any bone that develops within membranous tissue without previous cartilage formation; e.g. the clavicle and bones of the skull