Evolutionary changes of the two cranial elements of the posterior brain-case are observed (basisphenod and prootic) in the living species Natrix natrix since the Lower Pleistocene till the Recent. It seems to be apparent that the 'modern' pattern on the basicranial elements (particularly on the basisphenoid) of the living Natrix natrix, which is the direct descendant of the extinct Neogene species Natrix longivertebrata, were widely evolved as early as at the Plio-Pleistocene transition.