There is strong evidence in the literature for a correlation between the two parts of the red nucleus, magnocellular and parvocellular, and different functions. Unfortunately in the cat, the species most studied both physiologically and anatomically, there are no morphological criteria distinguishing the two portions. With quantitative techniques applied to Nissl preparations the neuronal population of the Red Nucleus has been studied in serial sections along the rostrocaudal axis of the mesencephalon of the cat. Statistical analysis of the data revealed a horizontal plane dividing the two portions of the nucleus with a high statistical significance level. This plane lies between the caudal two-thirds and the rostral third of the nucleus. Although in the model two portions can be distinguished, it is not possible to assign to either a single type of neuron, whether or considered in terms of shape or size.