**2. Variations in IVC anatomy**

In a study of the development of the IVC in the domestic cat (Felis domestica), Huntington and McLure(j) proposed a classification system for IVC anomalies based on abnormal regression or abnormal persistence of various embryonic veins. These investigators suggested that there could be up to 14 theoretical variations in the anatomy of the infrarenal IVC. They noted that 11 of the 14 variants had been observed in the domestic cat or in humans. In addition, these authors observed that other anomalies seen in humans, such as abnormal development of the pre-renal division of the IVC and persistence of the renal collar in the adult, could be explained on a similar basis.
