The Articulations. 



THE various bones of which the Skeleton consists are connected together at 

 different parts of their surfaces, and such connection is designated by the name 

 of Joint or Articulation. If the joint is immovable, as between the cranial and 

 most of the facial bones, the adjacent margins are applied in almost close 

 contact, a thin layer of fibrous membrane, the sutural ligament, and, at the base 

 of the skull, in certain situations, a thin layer of cartilage, being interposed. 

 Where slight movement is required, combined with great strength, the osseous 

 surfaces are united by tough and elastic fibre-cartilages, as in the joints of the 

 spine, the sacro-iliac, and interpubic articulations ; but in the movable joints, the 

 bones forming the articulation are generally expanded for greater convenience of 

 mutual connection, covered by an elastic structure, called cartilage, held together 

 by strong bands or capsules, of fibrous tissue, called ligament, and lined by a 

 membrane, the synovial membrane, which secretes a fluid that lubricates the 

 various parts of which the joint is formed, so that the structures which enter into 

 the formation of a joint are bone, cartilage, fibro-cartilage, ligament, and syriovial 

 membrane. 



Bone constitutes the fundamental element of all the joints. In the long bones, 

 the extremities are the parts which form the articulations ; they are generally 

 somewhat enlarged, consisting of spongy cancellous tissue, with a thin coating of 

 compact substance. In the flat bones, the articulations usually take place at the 

 edges ; and, in the short bones, by various parts of their surface. The layer of 

 compact bone which forms the articular surface, and to which the cartilage is 

 attached, is called the articular lamella. It is of a white color, extremely dense, 

 and varies in thickness. Its structure differs from ordinary bone-tissue in this 

 respect, that it contains no Haversian canals, and its lacunae are much larger than 

 in ordinary bone, and have no canaliculi. The vessels of the cancellous tissue, 

 as they approach the articular lamella, turn back in loops, and^do not perforate 

 it; this layer is consequently more dense, and firmer than ordinary bone, and 

 is evidently designed to form a steady and unyielding support for the articular 

 cartilage. 



Cartilage is firm, opaque, of a pearly-white or bluish- white color, in some 

 varieties yellow, highly elastic, readily yielding to pressure, and recovering its 

 shape when the force is removed, flexible, and possessed of considerable cohesive 

 power. In man, that form of cartilage which constitutes the original framework 

 of the body, and which in time becomes ossified throughout the greater part of its 

 extent, is called temporary cartilage. But there is another form of cartilage em- 

 ployed in the construction of the body that is not prone to ossify, viz., permanent 

 cartilage. This is found 1. In the joints, covering the ends of the bones 

 (articular cartilage) : 2. Forming a considerable part of the solid framework of 

 the chest (costal cartilages) : 3. Arranged in the form of plates or lamellas, of 

 greater or less thickness, which enter into the formation of the external ear, the 

 nose, the eyelids, the Eustachian tube, the larynx, and the windpipe (reticular 

 cartilage). They serve to maintain the shape of canals or passages, or to form 

 tubes that require to be kept permanently open without the expenditure of vital 

 force. 



Structure. Cartilage consists either of a parenchyma of nucleated cells, or the cells are 

 imbedded in an intercellular substance or matrix. The cells or cartilage corpuscles are contained 

 in hollow cavities or lacunae in the intercellular substance, which appear to be lined by a firm, 

 clear, or yellowish layer, the cartilage capsule. Under the influence of certain reagents, the 



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