Fifteen hundred palmar prints of normal persons and patients suffering from various diseases were studied and classified as to dermal ridge configurations at the base of digit IV, after the exclusion of main line C courses with endings at one of the palmar marginal regions. This classification scheme, based on the three classical reduction forms of line C (O,X(8),x), resulted in the differentiation of three main groups, A, B, and C. Within these main groups, pattern types with strong similarity were combined to subgroups allowing an easier documentation. Twin and family data were used to test whether the described pattern types, besides the classical abortive states O,X and x of line C (called special and intermediate forms), are heritable and for which of them a remarkable reduction tendency could be established. The results allow us to confirm the main grouping and the assumed reduction tendency of the special forms of group A.
