282 SYNDESMOLOGY 



joints i. 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 sub- 

 jected. 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 rota- 

 tion, 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 

 vertebrae. They form disks which are closely adherent to the opposed surfaces. 

 Each disk is composed of concentric rings of fibrous tissue, "with cartilaginous 

 laminae 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 w r hich form a thin coating to osseous 

 grooves through which the tendons of certain muscles glide. Small masses of fibro- 

 cartilage are also developed in the tendons of some muscles, where they glide 

 over bones, as in the tendons of the Peronaeus 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 laminae of adjacent vertebrae, 

 and the ligamentum nuchae 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 strata an external (stratum 

 fibrosuwi) composed of white fibrous tissue, and an internal (stratum synomale] 

 which is a secreting layer, and is usually described separately as the synovia! 

 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 



