Recent advances in the neurophysiology of the spinal cord, due largely to the use of microelectrodes, have increased the demand for a detailed knowledge of its minute anatomy, including the exact sites and mode of termination of the various contingents of afferent fibres to the spinal grey matter, among them the descending supraspinal fibre systems. Anatomical data of this kind are indispensable for functional interpretations and for the analysis of the structural and functional organization of the spinal cord. The observation of REXED (1952, 1954) that the grey matter of the feline spinal cord may be subdivided on a cytoarchitectonic basis into ten different laminae, presumably representing, at least in part, functionally different regions, should serve as a stimulus to attempt more precise analysis of the intrinsic organi zation of the spinal cord. Furthermore REXED'S laminae provide a common basis of reference of the sites of termination of afferent fibre systems to the spinal grey matter and the localization of single units recorded from in neurophysiological experiments, and thus promise useful correlations between anatomical and physiological observations and their functional interpretations.