I have never had any chance of examining the growthpost mortem, but the portions which I have removeden masseby operation have enabled me to make some investigations. The periosteum strips off readily, and under this is a thin shell of compact bone, which appears somewhat ridged on the side towards the periosteum. The rest of the tumor consists of cancellous bone. The whole swelling cuts readily with bone forceps and consists of quite soft bone. On making microscopical preparations there were signs of ossification in membrane proceeding under the periosteum, and the rest appeared like ordinary wide-meshed cancellous bone. The whole process appeared to be that of a slow “osteoplastic periostitis.”