Sagittal plane of the left kidney of a 10-year-old dog with chronic kidney disease for the measurement of the cortical and medullary ratio (C/M ratio): cortical thickness (C) was measured over a medullary pyramid, perpendicular to the capsule; medullary thickness (M) was measured from the renal hilum to the outer margin of the cortico-medullary junction. In this dog the C/M ratio was 0.64.