THE ARTICULATIONS IN GENERAL. 



173 



granular matter observed in the cells, it is not rare to find fat globules. The 

 nuclei of the cells vary from ^^V? *o Wmj o^ 8,n inch in diameter. The cells 

 multiply eudogenously.) 



The cartilage cells are insoluble in boiling water ; consequently, so far as 

 their chemical composition is concerned, they are distinct from the fundamental 

 substance. 



The diarthrodial cartilages have no vessels or nerves. 



The presence of cartilages of incrustation in the articulations is of the greatest 

 importance. When they are worn, absorbed, or transformed into bone in con- 

 sequence of certain articular maladies, the movements become painful and very 

 difficult. With regard to the part they play in the economy, it may be said that : 



1. They favour, by their smoothness, the gliding and displacement of the bones. 



2. They attenuate, by their suppleness and elasticity, the violent shocks to which 

 the articulations are exposed. S. They resist the wear and deformation of the 

 articular surfaces. 



Complementary Fibro-caetilages. — There are two kinds of complementary 

 fibro-cartilages. Some (interosseous) represent circular cushions which pad the 

 margins of certain cavi- 

 ties, filling up the notches ^' S- ^ ^ '^• 

 that might render these 

 imperfect. They in- 

 crease the depth of these 

 cavities, and protect their 

 borders from in j ury — for 

 example, the coxo-femo- 

 ral articulation. Others 

 (infer-articular) are in- 

 terposed between arti- 

 cular surfaces when these 

 do not exactly fit each 

 other — as when two opposing extremities are convex. It may be remembered 

 that the lateral tuberosities of each tibial surface present, for articulation with the 

 condyles of the femur, two convex diarthrodial faces, the coaptation of which is 

 rendered perfect by the interposition between each condyle and corresponding 

 tibial surface, of a crescent-shaped fibro-cartilage, which for this reason has been 

 named a meniscus. In other joints, these interarticular fibro-cartilages are 

 shaped like discs or biconcave lenses. There then result double diarthroses (Fig. 

 115, C, e) : example, the temporo-maxillary articulation. (Fibro-cartilage also 

 covers bony surfaces over which the tendons play, as on the trochlear surface of 

 the humerus, postero-inferior face of the navicular bone, and elsewhere. In 

 these situations it is named stratiform fibro-cartilage.) These organs are formed 

 sometimes by fibrous, at other times by cartilaginous tissue ; their mode of 

 association need not be referred to here, though it may be observed that the 

 cartilage is more particularly found in all those points where there is most 

 articular friction. They receive very few vessels, and it is questionable if they 

 have nerves. 



Ligaments. — These are bands which unite contiguous diarthrodial surfaces. 

 They are sometimes formed of white fibrous tissue, and sometimes of yellow ; 

 hence their division into two great classes of white and yeUoiv ligaments. 



a. The white ligaments are distinguished by the pearly whiteness of their 

 14 



FIBRO-CARTILAGE, MAGNIFIED 155 TIMES. 



Showing interlacement of fibrous fasciculi, with scattered 

 groups of cartilage-cells. 



