HYALINE CARTILAGE. Ixxxi 



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 connection 

 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 aflford 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 perma- 

 nent cartilages enter into the formation of the external ear, the nose, the 

 eyelids, the Eustachiau 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 attachment to moving muscles and connecting ligaments. 



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

 fibrous membrane named the perichondrium. 



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

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

 nated in a solid mass or matrix. (Figs, xxxix., XL. } and XLI.) 



The matrix is sometimes transparent, and to all appearance homogeneous ; 

 sometimes dim and very faintly granular, like ground glass : both these 

 conditions occur in hyaline cartilage, which may be regarded as the most 

 typical form of the tissue. Two varieties exist in which the matrix is per- 

 vaded to a greater or less extent by fibres. In the one named elastic or 

 yellow cartilage) the fibres are similar to those of elastic tissue ; in the 

 other, named jibro- cartilage, they are of the white kind as in ordinary 

 ligament. 



HYALINE CARTILAGE. 



lu 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-body of translucent, but sometimes finely granular- 

 looking substance, with a clear round nucleus and one or more nucleoli. 

 The cell-body lies in a cavity of the matrix, which, in its natural condition, 

 it entirely fills. This cavity is bounded and inclosed by a transparent 

 capsule, which is seldom obvious to the eye, for it coheres intimately with 

 the surrounding matrix, with which it agrees in nature, and cannot usually 

 be distinguished without the aid of re-agents. The capsule has been 

 regarded as a secondary cell-wall and compared to the cellulose wall of 

 vegetable cells ; while the body which it contains is, on the same view, con- 

 sidered to be homologous with the primordial utricle and its contents. But 

 the same doubt prevails here as in the case of vegetables, as to the existence 

 of a proper membrane (the utricle) immediately investing the substance of the 

 cell. (See page xiv, and figures vm. and ix.) 



In thin slices of young cartilage the capsules may be freed from the matrix by 

 means of concentrated mineral acids, and can then be shown as distinct vesicles 



