Using a phylogenic classification of the spine, one can identify precisely the numerical location of any vertebra or disc, including vertebrae with junctional anomalies at transitional zones. Such precision permitted comparisons of myelographic reports of sites of disc disease with the actual levels of extradural deformities and of charted levels of disc operations with the actual levels of disc curettements. Among 100 patients there were 33 with phylogenic or junctional departures from the human mode. Among these 33 there was a combined total of 18 identification errors, and there were four entries at incorrect levels. Preoperative landmarking would appear to be obligatory.