50 ELEMENTAEY TISSUES. 



the deeper layer of the epidermis, or the so-called rete 

 mucosum. 



The pigmentary matter is a very insoluble compound 

 of carbon, hydrogen, nitrogen and oxygen, the carbon 

 largely predominating ; besides, there is a small quantity 

 of saline matter. 



The uses of pigment in most parts of the body are not 

 clear. In the eyeball it is evidently intended for the 

 absorption of superfluous rays of light. 



Cartilage. 



Cartilage or gristle exists in different forms in the 

 human body, and has been classified under two chief 

 heads, namely, temporary and permanent cartilage ; the 

 former term being applied to that kind of cartilage which, 

 in the foetus and in young subjects, is destined to be con- 

 verted into bone. The varieties of permanent cartilage 

 hav,e been arranged in three classes, namely, the cellular, 

 the hyaline, and the fibrous cartilages, the last-named, 

 being again capable of subdivision into two kinds, 

 namely, elastic or yellow cartilage, and the so-called fibro- 

 cartilage. 



Elastic cartilage, however, contains fibres, and fibro- 

 cartilage is more or less elastic ; it will be well, therefore, 

 for distinction's sake to term those two kinds white fibro- 

 cartilage and yellow fibro-cartilage respectively. 



The accompanying table represents the classification of 

 the varieties of cartilage : 



i. Temporary. 



A. Cellular. 



2. Permanent. WHte fibro _ cartilage . 



- Flbrous - { Vellow fibro-cartilage. 



All kinds of cartilage are composed of cells imbedded 

 in a substance called the matrix ; and the apparent 

 differences of structure met with in the various kinds of 



