What important discovery is John Hunter credited with?

John Hunter is most notably recognized for his work with what is known as Hunter's Canal, which is an anatomical structure that plays a significant role in the vascular system of the leg. This canal allows important vessels to pass through the thigh and provides relevant insights into anatomy and biomechanics.

Hunter's contribution to this area is essential for understanding the circulatory and lymphatic systems, although he is also celebrated for other achievements in medical science, including early studies that contributed to the understanding of blood circulation and surgical procedures.

While the other options address important concepts in anatomy and physiology, they are most closely associated with different historical figures or require contextual knowledge beyond Hunter's specific contributions. Hunter's Canal represents a clear and identifiable discovery attributed to John Hunter, thereby making it the correct response in this question.