THE STRUCTURE OF THE ELEMENTARY TISSUES. 41 



human body investing the articular ends of bones, and forming the 

 costal cartilages, the nasal cartilages, and those of the larynx with the 

 exception of the epiglottis and cornicula laryngis, as well as those of the 

 trachea and bronchi. 



Structure. Like other cartilages it is composed of cells imbedded in 

 a matrix. The cells, which contain a nucleus with nucleoli, are irregu- 

 lar in shape, and generally grouped together in patches (Fig. 45). The 

 patches are of various shapes and sizes, and placed at unequal distances 

 apart. They generally appear flattened near the free surface of the mass 

 of cartilage in which they are placed, and more or less perpendicular to 

 the surface in the more deeply-seated portions. 



The matrix of hyaline cartilage has a dimly granular appearance like 

 that of ground glass, and in man and the higher animals has no apparent 

 structure. In some cartilages of the frog, however, even when examined 

 in the fresh state, it is seen to be mapped out into polygonal blocks or 

 cell-territories, each containing a cell in the centre, and representing 

 what is generally called the capsule of the cartilage cells (Fig. 46). 

 Hyaline cartilage in man has really the same structure, which can be 

 demonstrated by the use of certain reagents. If a piece of human hya- 

 line cartilage be macerated for a long time in dilute acid or in hot water 

 95-113 F. (35 to 45 C.), the matrix, which previously appeared 

 quite homogeneous, is found to be resolved into a number of concentric 

 lamellae, like the coats of an onion, arranged round each cell or group of 

 cells. It is thus shown to consist of nothing but a number of large 

 systems of capsules which have become fused with one another. 



The cavities in the matrix in which the cells lie are connected to- 

 gether by a series of branching canals, very much resembling those in 

 the cornea: through these canals fluids may make their way into the 

 depths of the tissue. 



In the hyaline cartilage of the ribs, the cells are mostly larger than 

 in the articular variety, and there is a tendency to the development of 

 fibres in the matrix (Fig. 47). The costal cartilages also frequently be- 

 come calcified in old age, as also do some of those of the larynx. Fat- 

 globules may also be seen in many cartilages (Fig. 47). 



In articular cartilage the cells are smaller, and arranged vertically in 

 narrow lines like strings of beads. 



Temporary Cartilage. In the foetus, cartilage is the material of 

 which the bones are first constructed; the " model " of each bone being 

 laid down, so to speak, in this substance. In such cases the cartilage is 

 termed temporary. It closely resembles the ordinary hyaline kind; 

 the cells, however, are not grouped together after the fashion just 

 described, but are more uniformly distributed throughout the matrix. 



A variety of temporary hyaline cartilage which has scarcely any 



