Division of the thorax into four quadrants for pulmonary pattern and severity identification is illustrated on a lateral radiograph of the thorax of a 69-day-old Jersey heifer calf. The line parallel with the ventral aspect of the trachea divides the thorax into a dorsal and ventral half. The line parallel with the caudal border of the 5th rib divides the thorax into a cranial and caudal half.