The specimen presented is that of a very rare anomaly, showing congenital absence of a separate pericardial sac, the heart being contained in the same serous cavity as the left lung. It was obtained by Dr. W. A. Burr, who was called to the city morgue to undertake the postmortem examination of a middle-aged man who had died suddenly. When the thorax was opened, Dr. Burr was surprised to find the heart and the left lung occupying a common cavity. As he realized the rarity and value of what he had found, he removed all the thoracic viscera, the diaphragm and what remained of the pleural sacs en masse and presented the specimen to the department of anatomy of the University of Toronto. REPORT OF CASE The man from whom these viscera were obtained was aged 52, of medium height and well developed. He was unmarried and lived alone and