The articular ends are the solid supports and the effectors of joint motion. They are able to serve as such by having mutually complementary osseous configurations and by merging on their surface with a caplike layer of hyaline cartilage. The latter owes its functional capacity partly to its ground substance, whose main constituents are proteoglycans. The characteristic part of the proteoglycans are the glycosaminoglycans [1350, 1352] onto whose negatively charged anions a large proportion of water is attracted [1034, 1035]. The other essential constituent of the articular cartilage is a firmly anchored collagenous fibrillar network (Figs. 5, 7) which enmeshes the ground substance. Due to these components the articular cartilage possesses a high intrinsic pressure and is able to resist the external pressure which arises when two opposing articular surfaces are moved along one another.