Structures that are cavities, depressions or openings in bone such as a sinus, fossa, canal or foramen will allow x-rays to penetrate through them and expose the receptor. These areas will appear radiolucent or black on radiographic images. Structures that are bony in origin absorb or stop the penetration of the x-rays and, therefore, do not reach the receptor. These areas appear radiopaque or white on radiographic images. Some structures partially absorb radiation and are represented in varying degrees of radiopacity.