Final answer:
The hyoid bone can appear as a double image due to its unique independent positioning in the upper neck, where it is suspended by muscles and does not directly join with other bones.
Step-by-step explanation:
The appearance of the double image of the hyoid bone is due to its unique positioning in the body. The hyoid bone is a small U-shaped structure located in the upper neck, which is held in place by muscles and does not physically articulate with any other bones. It is significant because it provides attachments for muscles acting on the tongue, larynx, and pharynx, and plays an important role in swallowing and speaking. Unlike parts of the skeleton that create a clear image on X-rays due to their pronounced structures or connections with other bones, the hyoid's independent position means it might be less distinctly visualized, potentially leading to an appearance that can be mistaken as double. However, it should not overlap with the mandible in proper imaging unless positioned in a way that creates an overlapping image due to the angle of the X-ray.