Heterura

Heterura refers to a condition where an individual possesses two tails. This is an extremely rare congenital anomaly. The tails can vary in appearance, from being fully formed and distinct to being fused or vestigial. The underlying cause is often related to developmental issues during embryonic growth, specifically concerning the caudal regression that forms the tailbone. In some cases, this process may be incomplete, leading to the development of supernumerary caudal appendages.

While heterura has been documented in various species, including some reptiles and mammals, its occurrence in humans is exceedingly rare, with only a handful of documented cases throughout history. The exact genetic or environmental factors contributing to this anomaly are not fully understood, but it is believed to be a complex interplay of developmental signals. The presence of a tail, let alone two, in humans is considered a form of caudal appendage, and heterura represents an extreme manifestation of this phenomenon. The functional significance of these tails, if any, varies greatly depending on their development and integration with the body's systems. Medical attention is typically sought to assess the health implications and potential need for surgical intervention, though many cases are benign.