Which structure is referred to as the "horse's tail" in the spinal cord?

The structure commonly referred to as the "horse's tail" in the spinal cord is the cauda equina. This term describes a bundle of spinal nerves and spinal nerve rootlets situated in the lower part of the vertebral canal. The cauda equina resembles a tail due to its fan-like appearance, and it is formed because, in the adult human, the spinal cord does not extend all the way down to the end of the vertebral column; instead, it ends at the conus medullaris at about the level of the first or second lumbar vertebra. Below this point, the nerve roots continue to travel downwards within the lumbar and sacral regions, resembling the tail of a horse.

The cauda equina plays a crucial role in providing the nerve supply to the pelvic organs and lower limbs, which makes its functionality vital for movements and sensations in these regions. The other structures mentioned, while significant in their own right, do not exhibit this particular arrangement or serve this descriptive purpose. Understanding the anatomy and function of the cauda equina is essential for recognizing its importance in both health and injury contexts.