Henry Gray (18251861). Anatomy of the Human Body. 1918.
jointsi. e., in those joints which are most exposed to violent concussion and subject to frequent movement. Their uses are to obliterate the intervals between opposed surfaces in their various motions; to increase the depths of the articular surfaces and give ease to the gliding movements; to moderate the effects of great pressure and deaden the intensity of the shocks to which the parts may be subjected. Humphry has pointed out that these interarticular fibrocartilages serve an important purpose in increasing the varieties of movement in a joint. Thus in the knee joint there are two kinds of motion, viz., angular movement and rotation, although it is a hinge joint, in which, as a rule, only one variety of motion is permitted; the former movement takes place between the condyles of the femur and the interarticular cartilages, the latter between the cartilages and the head of the tibia. So, also, in the temporomandibular joint, the movements of opening and shutting the mouth take place between the fibrocartilage and the mandible, the grinding movement between the mandibular fossa and the fibrocartilage, the latter moving with the mandible.
2. The Connecting Fibrocartilages are interposed between the bony surfaces of those joints which admit of only slight mobility, as between the bodies of the vertebræ. They form disks which are closely adherent to the opposed surfaces. Each disk is composed of concentric rings of fibrous tissue, with cartilaginous laminæ interposed, the former tissue predominating toward the circumference, the latter toward the center.
3. The Circumferential Fibrocartilages consist of rims of fibrocartilage, which surround the margins of some of the articular cavities, e. g., the glenoidal labrum of the hip, and of the shoulder; they serve to deepen the articular cavities and to protect their edges.
4. The Stratiform Fibrocartilages are those which form a thin coating to osseous grooves through which the tendons of certain muscles glide. Small masses of fibrocartilage are also developed in the tendons of some muscles, where they glide over bones, as in the tendons of the Peronæus longus and Tibialis posterior.
The distinguishing feature of cartilage chemically is that it yields on boiling a substance called chondrin, very similar to gelatin, but differing from it in several of its reactions. It is now believed that chondrin is not a simple body, but a mixture of gelatin with mucinoid substances, chief among which, perhaps, is a compound termed chondro-mucoid.
Ligaments.Ligaments are composed mainly of bundles of white fibrous tissue placed parallel with, or closely interlaced with one another, and present a white, shining, silvery appearance. They are pliant and flexible, so as to allow perfect freedom of movement, but strong, tough, and inextensible, so as not to yield readily to applied force. Some ligaments consist entirely of yellow elastic tissue, as the ligamenta flava which connect together the laminæ of adjacent vertebræ, and the ligamentum nuchæ in the lower animals. In these cases the elasticity of the ligament is intended to act as a substitute for muscular power.
The Articular Capsules.The articular capsules form complete envelopes for the freely movable joints. Each capsule consists of two strataan external (stratum fibrosum) composed of white fibrous tissue, and an internal (stratum synoviale) which is a secreting layer, and is usually described separately as the synovial membrane.
The fibrous capsule is attached to the whole circumference of the articular end of each bone entering into the joint, and thus entirely surrounds the articulation.
The synovial membrane invests the inner surface of the fibrous capsule, and is reflected over any tendons passing through the joint cavity, as the tendon of the Popliteus in the knee, and the tendon of the Biceps brachii in the shoulder. It is composed of a thin, delicate, connective tissue, with branched connective-tissue corpuscles. Its secretion is thick, viscid, and glairy, like the white of an egg, and