In this work a statistical study is made of the final outcome of the quantification of the nerve cell labelling in the adult, after prenatal injection of tritiated thymidine. This outcome is presented in the form of histograms which are the superposition of elementary Poisson distributions. A theoretical model, based on Probability theory, has been developed explaining the experimental outcome. Studying the final histograms of a defined region, according to this model, we can find out the number and the importance of the constitutive cell generations (chronology). From the graphic study of the percentage of labelled cells and that of the average of grains, the characteristics of the stratification of the neuronic populations/architectony) can be defined. All these notions have been gathered into a new concept: chronoarchitectony. This concept has also been applied to the neocortex. The results show that there is a strong interpenetration of the different cell generations in a given layer. The cortical neuronic production is a continuous phenomenon and there is no correspondence with the discontinuity of the cortical layers.