LIGAMENTS 261 



usually found in those joints which are most exposed to violent concussion and subject to fre- 

 quent movements. Their use is to maintain the apposition of the opposed surfaces in their 

 various motions; to increase the depth of the articular surfaces and give ease to the gliding 

 movement; to moderate the effects of great pressure and deaden the intensity of the shocks to 

 which the parts may be subjected. Humphry ha. r pointed out that these intra-articular fibro- 

 cartilages serve an important purpose in increasing the variety of movements 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 articular cartilages, the 

 latter between the cartilages and the head of the tibia. So>, also, in the temporomandibular 

 joint, the upward and downward movement of opening and shutting the mouth takes place 

 between the fibrocartilage and the mandible, the grinding movement between the glenoid cavity 

 and the fibrocartilage, the latter moving with the mandible. 



Intra-articular cartilages may divide the joint into two distinct cavities, as in the temporo- 

 mandibular articulation. The periphery of an articular cartilage is attached particularlv to 

 the capsule, and may also be attached to the nonarticular portion of the bone. The semilunar 

 cartilages of the knee resemble tendon more than they do cartilage. The fibres are arranged 

 in dense, more or less parallel bundles, separated by small, scattered hyaline cells, and the disks 

 are attached to the bone by thin layers of hyaline cartilage. 



'2. The connecting fibre-cartilages are interposed between the bony surfaces of those joints 

 which admit of only slight mobility, as between the bodies of the vertebrae and between the 

 pubic bones. They form disks which adhere closely to both of the opposed surfaces, and are 

 composed of concentric rings of fibrous tissue, with cartilaginous laminae interposed, the former 

 tissue predominating toward the circumference, the latter toward the centre. 



3. The circumferential fibrocartilage s consist of a rim of fibrocartilage, which surrounds the 

 margin of some of the articular cavities, as the cotyloid cavity of the hip and the glenoid cavity 

 of the shoulder; they serve to deepen the articular surface, and to protect its edges. 



Elastic cartilage, although not utilized in joints, may be considered here. It is surrounded 

 by a perichondrium, and its matrix differs from the preceding varieties in being composed 

 chiefly of yellow elastic tissue. It is found in the pinna of the ear, Eustachian tube, epiglottis, 

 and small cartilages of the larynx. It does not ossify or calcify. 



Cartilage, in the adult, is an avascular tissue, and although vessels at times are seen in the 

 costal cartilages, they do not nourish it, as no branches are given off. Nerves are likewise 

 absent. 



Ligaments consist of bands of various forms, serving to connect the articular 

 extremities of bones, and are composed mainly of coarse bundles of very 

 dense, white, fibrous tissue placed parallel with, or closely interlaced with, one 

 another, and presenting a white, shining, silvery aspect. A ligament is pliant 

 and flexible, so as to allow of the most perfect freedom of movement, but it is 

 strong, tough, and inextensile, so as not readily to yield under the most severely 

 applied force; it is consequently w r ell adapted to serve as the connecting medium 

 between the bones. Some ligaments consist entirely of yellow elastic tissue, as 

 the ligamenta subflava, which connect together the adjacent arches of the verte- 

 bra? in man, and the ligamentum nuchae in the lower animals are composed of 

 yellow elastic tissue. In these cases it will be observed that the elasticity of the 

 ligament is intended to act as a substitute for muscular power. 



Synovial membrane is a thin, delicate, serous membrane, arranged in its 

 simplest form like a short, wide tube, attached by its open ends to the margins 

 of the articular cartilages and covering the inner surfaces of the various ligaments 

 which connect the articulating surfaces, so that, along with cartilages, it completely 

 encloses the joint-cavity. Its transudate is thick, viscid, and glairy, like the 

 white of an egg, hence it is termed synovia. It is composed of a single layer of 

 endothelial cells resting upon a thin layer of fibroelastic (subendothelial) tissue. 

 The synovial membranes found in the body admit of subdivision into three kinds 

 articular, bursal, and vaginal. 



Articular synovial membrane is found in every freely movable joint. It lines the capsule 

 of the joint and is reflected upon the nonarticular intracapsular portion of the bones which 

 enter into the formation of the joint. In the fetus this membrane is said, by Toynbee, to 



