In the context of anatomy, what does the symbol "X" commonly represent?

In the context of anatomy, the symbol "X" often represents a specific type of imaging technique known as an X-ray. X-rays are a form of electromagnetic radiation that can penetrate through various tissues in the body, allowing for the visualization of bones and skeletal structures. This makes option B the correct choice, as it directly relates to how an X-ray image is produced, often resembling a ray-like representation of bone structures in the anatomical context.

The other options do not fit within this context. For instance, while tissues, muscular structures, and joints are essential components of anatomy, they do not convey the same imaging implication that "X" does in the context of understanding skeletal imagery. Specifically, there is no established convention for representing tissues, muscles, or joints with the letter "X," making them less relevant to the question at hand.