CARTILAGE. 51 



CARTILAGE. 



*r 



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 air-passages, nostrils, and ears, which are to be kept 

 permanently open. In the foetus at an early period the greater part of the skele- 

 ton 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 which is called permanent. 



Cartilage is divided, according to its minute structure, into true or hyaline 

 cartilage, fibrous or fibro-cartilage. and yelloir or elastic or reticular cartilage. 

 Besides these varieties met with in the adult human subject, there is a variety 

 called cellular cartilage* which consists entirely, or almost entirely, of cells, united 

 in some eases by a network of very fine fibres, in other cases apparently destitute 

 of any intercellular substance. This is found in the external ear of rats, mice, 

 and some other animals, and is present in the chorda dorsalis of the human 

 embryo, but is not found in any other human structure. The various cartilages 

 in the body are also classified, according to their function and position, into 

 articular, interarticular. costal, and membraniform. 



Hyaline cartilage, which may be taken as the type of this tissue, consists of a 

 gristly mass of a firm consistence, but of considerable elasticity and of a pearly- 

 bluish color. Except where it coats the articular ends of bones, it is enveloped 

 in a fibrous membrane, the perichondrium, from the vessels of which it imbibes 

 its nutritive fluids, being itself destitute of blood-vessels : nor have any nerves 

 been traced into it. Its intimate 

 structure is very simple. If a thin 

 slice is examined under the micro- 



e. 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. 22). The cells, when 

 arranged in groups of two or more, 

 have generally a straight outline 



-.1 IK.. *!. Human cartilage-cells, from the cricoid carti- 



wnere tne\ are in contact \\itn eacli i age- Magnified sao times, 

 other, and in the rest of their cir- 

 cumference are rounded. The cell-contents consist of clear translucent proto- 

 plasm containing minute granules, and imbedded in this are one or two nuclei, 

 having usually a granular appearance, but occasionally being clear and occupied 

 by one or more nucleoli. The cells are imbedded in cavities in the matrix, called 

 <->irtil,_i<je l,-i<-uim\ which are lined bv a distinct transparent membrane called 

 the capsule. Each lacuna is genevallv occupied by a single cell, but during the 

 division of the cells it may contain two, four, or eight cartilage-cells. By 

 boiling the cartilage for some hours and treating it with concentrated mineral 

 acid, the capsule may be freed from the matrix, and can then be demonstrated as a 

 distinct vesicle containing the cells. By exposure to the action of an electric shock 

 the cell assumes a jagged outline and shrinks away from the interior of the 

 capsule. 



The matrix is transparent and apparently without structure, or else presents 

 a dimly granular appearance, like ground glass. Some observers have shown 

 that the matrix of hyaline cartilage, and especially the articular variety, after 

 prolonged maceration, can be broken up into fine fibrils. These fibrils are prob- 

 ably of the same nature, chemically, as the white fibres of connective tissue. It 

 is believed by some histologists that the matrix is permeated by a number of 

 fine channels, which connect the lacunae with each other, and that these canals 

 communicate with the lymphatics of the perichondrium, and thus the structure is 

 permeated with a current of nutritious fluid. 



