In anatomical terminology, what are viscera?

Viscera refers specifically to the internal organs located within the main body cavities, such as the thoracic cavity and the abdominal cavity. This term is primarily associated with the organs involved in various bodily functions, including the heart, lungs, liver, intestines, and others found within these cavities. Understanding this terminology is crucial in fields like medicine and anatomy, as it highlights the distinction between internal structures and external body parts.

The other options do not accurately describe the term viscera. For instance, external structures would include skin and limbs, supportive tissues involve bones and connective tissues, and muscle systems pertain to muscular structures responsible for movement. Therefore, the correct choice encapsulates the essence of what viscera truly are—essentially, the internal organs that play key roles in physiological processes.