and function and that the neoplasm results not from a single disordered cell, but from the activity of this disordered system. As a neoplasm grows it tends to strip the periosteum to cause reactive bone formation.
Many bony tumours, I believe, are a combination of neoplastic and reactive bone. Right-angle spiculation, so commonly seen in body tumours, is much more likely to be reactive than neoplastic. There is, in bony tumours as in neoplasms elsewhere in the body, a wide variance in the histological picture: not only from one growth to another but from one part of a growth to another part. The impression that I gained from this series is that every phase in the development of bone is paralleled by its neoplastic counterpart.
SUMlMARY
Twenty cases of different types of osteomata of the skull are described and the histological pictures portrayed in some cases. The life-history of a tumour has been known for 10-20 years, and an attempt is made to give some account of histopathological correlation to the various types of neoplasms that arise primarily in the bone-forming organs of the skull. I would like to thank Mr. R. Ridley of the Department of Photography, King's College, Newcastle upon Tyne, for the quality of the illustrations, and Miss M. Bousfield and Miss A. Cairns for their help with the preparation of this paper. I am also grateful for a grant from the Research Fund of the Royal Victoria Infirmary. REFERENCES ABBOTT, K. H., and COURVILLE, C. B. (1939)~ Bull. Los Angeles neurol. SOC., 4, 101. _ _ --(1945), Zbid., 10, 19.