CAETILAGE. 



CARTILAGE. 



This is the well-known substance commonly called " gristle." The 

 following are its more obvious characters. AVhen in mass, it is opaque 

 and of a pearly or bluish white colour, in some varieties yellow ; but in 

 thin slices it is translucent. Although it can be easily cut with a sharp 

 knife, it is nevertheless of very firm consistence, but at the same time 

 highly elastic, so that it readily yields to pressure or torsion, and 

 immediately recovers its original shape when the constraining force 

 is withdrawn. By reason of these mechanical properties, it is rather 

 extensively used in the construction of the body. Its specific gravity 

 is 1-15. 



In the early embryo the skeleton is, in great part, cartilaginous ; but 

 the cartilage forming its different pieces, which have the outward form 

 of the future bones, in due time undergoes ossification or gives place to 

 bone, in the greater part of its extent at least, and hence this variety 

 of cartilage is named " temporary." 



Of the permanent cartilages a great many are in immediate con- 

 nection with bone, and may be still said to form part of the skeleton. 

 The chief of these are the articular and the costal cartilages ; the 

 former cover the ends or surfaces of bones in the joints, and afford 

 these harder parts a thick springy coating, which breaks the force of 

 concussion and gives ease to their motions ; the costal or rib-cartilages 

 form a considerable part of the solid framework of the thorax, and 

 impart elasticity to its walls. Other permanent cartilages enter into 

 the formation of the external ear, the nose, the eyelids, the Eustachian 

 tube, the larynx, and the windpipe. They strengthen the substance of 

 these parts without undue rigidity ; maintaining their shape, keeping 

 open the passages through them where such exist, and giving attach- 

 ment to moving muscles and connecting ligaments. 



Cartilages, except those of the joints, are covered externally with a 

 fibrous membrane named the pcricliondrimn. 



When a very thin slice of cartilage is examined with the microscope, 

 it is seen to consist of nucleated cells, also named cartilage-corpuscles, 

 disseminated in a solid mass or matrix. (Fig. 42.) 



The matrix is sometimes transparent, and to all appearance homo- 

 geneous ; sometimes dim and very fliintly granular, like ground glass : 

 both these conditions occur in hjaUm carttlafie, which may be regarded 

 as the most typical form of the tissue. Two varieties exist in which 

 the matrix is pervaded to a greater or less extent by fibres. In the one 

 named ehsfic or yelloiv cartiJago, the fibres are similar to those of elastic 

 tissue ; in the other, named fihro-cartiJagc, they are of the white kind 

 as in ordinary ligament. 



HYALINE CARTILAGE. 



In hyaline cartilage the matrix, as just stated, is uniform and, in the 

 normal state, free from fibres. The cells consist of a rounded, oval, 

 or bluntly angular cell-hodij of translucent, but sometimes finely gran- 

 ular-looking substance (fig. 42, //), with a round nucleus {n), which is 

 either clear or of a coarsely granular appearance, and one or more 

 niicJeoU. The cell-body lies in a cavity of the matrix, which, in its 

 natural condition, it entirely fills. This' cavity is bounded and inclosed 



