Which of the following bones in the face are the only ones that aren't a pair of bones?

Choice A reason: Protection of the brain is the primary function of cranial bones. They form the skull, which encases and shields the brain from mechanical injury.

Choice B reason: Muscles attach to facial bones, not cranial bones. While cranial bones may serve as attachment sites for some muscles, this is not their main function.

Choice C reason: The introduction of food into the digestive system involves the mouth and associated facial structures, not cranial bones.

Choice D reason: Passageways for respiratory gases are formed by facial bones and nasal structures, not the cranial bones.

Choice E reason: Special sense organs such as the eyes, ears, and nose are housed in facial bones and cavities, not primarily in cranial bones. Cranial bones protect the brain, not sensory organs.

Choice A reason: Epiphysis and diaphysis refer to regions of a long bone—the ends and shaft respectively—not to the coverings of bone surfaces.

Choice B reason: This reverses the anatomical regions but still does not address the coverings of bone surfaces.

Choice C reason: Compact bone and spongy bone are types of bone tissue, not the membranes that line or cover bone surfaces.

Choice D reason: The periosteum is a dense fibrous membrane that covers the external surface of bones, providing attachment points for tendons and ligaments and housing blood vessels and nerves. The endosteum lines the internal surfaces, including the medullary cavity, and plays a role in bone growth and remodeling.

Choice E reason: This reverses the correct anatomical relationship. The endosteum lines the internal surface, not the external.