While studying a series of films of the œsophagus taken in the routine right anterior oblique position, an abnormal shadow was occasionally detected, always in approximately the same location. Its visualisation appeared to depend on the angle through which the patient was rotated. This angle seemed to vary in each individual case, but if very distinct, the shadow could be seen on screen examination and shown on films taken in the optimum position thus determined. In other cases, the degree of rotation giving the best view of the œsophagus happened to coincide with the critical angle necessary to demonstrate the abnormal shadow, and it therefore appeared more or less distinctly on the routine films. The shadow in question is a small oval, about one-half inch in its longest diameter and of the same density as the aortic shadow. It lies in contact with the right postero-lateral aspect of the œsophagus at the level of the fourth or fifth thoracic vertebra. Above and below it is continuous with that part of th...