In most cases of arthritis the inflammation affects, more or less, all the structures which enter into the construction of the joint. The irritant is usually present in the joint itself, and is distributed over it, with the synovial fluid, by the movements of the joint. We may expect, therefore, that the synovial membrane and the cartilage, as they cover the surface, will in most cases be primarily affected. The cartilage, being non-vascular, is less liable to inflammatory changes than the synovial membrane, which in most cases is primarily and chiefly engaged, especially in acute inflammations. But in chronic cases the irritation extends beyond these structures to the ends of the bones, to the neighbouring periosteum, and even to the ligaments.