SYNDESMOLOGY. 



THE bones of the skeleton are joined to one another at different parts of their 

 surfaces, and such connections are termed Joints or Articulations. Where 

 the joints are immovable, as in the articulations between practically all the bones 

 of the skull, the adjacent margins of the bones are almost in contact, being separated 

 merely by a thin layer of fibrous membrane, named the sutural ligament. In certain 

 regions at the base of the skull this fibrous membrane is replaced by a layer of car- 

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

 surfaces are united by tough and elastic fibrocartilages, as in the joints between the 

 vertebral bodies, and in the interpubic articulation. In the freely movable joints 

 the surfaces are completely separated; the bones forming the articulation are ex- 

 panded for greater convenience of mutual connection, covered by cartilage and 

 enveloped by capsules of fibrous tissue. The cells lining the interior of the fibrous 

 capsule form an imperfect membrane the synovial membrane which secretes 

 a lubricating fluid. The joints are strengthened by strong fibrous bands called 

 ligaments, which extend between the bones forming the joint. 



Bone. 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; and consist 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 at various parts of their surfaces. The 

 layer of compact bone which forms the joint surface, and to which the articular 

 cartilage is attached, is called the articular lamella. It differs from ordinary 

 bone tissue in that it contains no Haversian canals, and its lacunae are larger 

 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 con- 

 sequently denser and firmer than ordinary bone, and is evidently designed to form 

 an unyielding support for the articular cartilage. 



Cartilage. Cartilage is a non-vascular structure which is found in various 

 parts of the body in adult life chiefly in the joints, in the parietes of the thorax, 

 and in various tubes, such as the trachea and bronchi, nose, and ears, which require 

 to be kept permanently open. In the fetus, at an early period, the greater part 

 of the skeleton is cartilaginous; as this cartilage is afterward replaced by bone, 

 it is called temporary, in contradistinction to that which remains unossified during 

 the whole of life, and is called permanent. 



Cartilage is divided, according to its minute structure, into hyaline cartilage, 

 white fibrocartilage, and yellow or elastic fibrocartilage. 



Hyaline Cartilage. Hyaline cartilage consists of a gristly mass of a firm consist- 

 ence, but of considerable elasticity and pearly bluish color. Except where it coats 

 the articular ends of bones, it is covered externally by a fibrous membrane, the 

 perichondrium, from the vessels of which it imbibes its nutritive fluids, being itself 

 destitute of bloodvessels. It contains no nerves. Its intimate structure is very 

 simple. If a thin slice be examined under the microscope, it will be found to consist 

 of cells of a rounded or bluntly angular form, lying in groups of two or more in 

 a granular or almost homogeneous matrix (Fig. 292). The cells, when arranged 

 in groups of two or more, have generally straight outlines where they are in contact 



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