1. A series of twenty-one cases of synovial tumour is tabled and the histological appearances are discussed.

2. The characteristic histological forms, (a) mucin formation, (b) synovial spaces, (c) endothelial and "gland" spaces and (d) epithelium-like tissue, are described.

3. These all arise by differentiation of connective tissue cells which occur throughout the connective tissue part of the limbs.

4. Though more commonly found in regions where synovial membrane is present, they are not confined to such special areas.

5. The tumours are classified on a histological and not a histogenetic basis.