1 . Twenty patients with fibrous dysplasia, confirmed histologically, are reported and discussed in regard to classification, etiology, pathogenesis and treatment. The various fibrous or fibrocystic lesions of bone are characterised briefly for purpose of contrast, and the position of fibrous dysplasia in this heterogeneous collection is suggested.

2. The classification of fibrous dysplasia based on the degree of skeletal involvement is used, and the diagnostic, therapeutic and prognostic implications of this classification emphasised. The authors endorse the opinion that fibrous dysplasia is a developmental defect. Clinical, histological and radiographic evidence is presented to point to the distinct evolution of the monostotic lesions, to which a positive and aggressive approach is recommended.

Benign giant-cell synovioma, the most frequent example of which is the well-known myeloid tumour of tendon sheaths, is used as a text for the discussion of the true significance of the so-called "xanthoma" cell. These cells are the result of the phagocytosis of cholesterol esters and are of varied histogenesis. Some are undoubtedly of neoplastic origin; most of them are not, being usually histiocytic, fibrocytic, serosal or endothelial. There is no such thing as a specific xanthoma cell.

The term "xanthosis" might well be used to designate this process of infiltration of tissue with cholesterol fat, and the prefix "xantho-" or the adjective "xanthic" in tumour terminology, as for example in "fibro-xantho-sarcoma," "xanthic neurofibroma," and so on.