Mongoose Lemur (_Lemur mongoz_) ♂ . Sacculo-fusiform dilatation of esophagus, probably congenital, with adjacent fibrosis of lung. In poor condition for several years but recovered satisfactorily from a bad cut inflicted by cage-mates. At autopsy the general condition is poor, hair missing in spots, all skin dry and atrophic with patches of keratotic dermatitis. All tissues anemic, muscles lusterless. Right lung collapsed, brown and pink, spotted with anthracosis. Left lung pushed forward and to left by a mass in the posterior mediastinum. Lower lobe in its posterior portion is adherent to esophageal mass. Lower half of this lobe beginning where bronchus ends and extending over anterior-posterior surfaces shows marked fibrotic processes and at one point in tissue between end of bronchus and adherent esophagus there is no lung tissue remaining. No recent consolidations. Bronchial lymph nodes, small, firm homogeneous pale brown with specks of anthracosis. Heart contracted, normal in size, firm red-brown. Aorta is firmly adherent to esophageal mass where bronchus crosses it. The lower half of the esophageal from the hilum of the lung to the cardia is the seat of a dilatation, fusiform for the most part, but with a saccular portion anteriorly. This latter presses the left bronchus upward and heart forward. The wall of the tube is slightly irregularly thickened but there is no cicatrix and mucosa shows slight hypertrophic condition. A large mass of food occupies the dilatation. Stomach is empty save for gas. Mucosa is soft, smooth, pale pink. Duodenum shows slight swelling of the rather pale yellow submucosa and mucosa, but the tips of the villi are injected. Intestine contains only a little slimy mucus. Large intestine contains a mass of constipated feces. The esophageal dilatation seems to have been congenital although it is barely possible that the fibrosing pneumonitis and pleuritis may have aided and caused it by traction. It has been doubtless the cause of the animal’s inanition.