CARTILAGE. BONE. TEETH. 27 



the fundamental substance of the tissue. Sometimes 

 this capsule includes but one cell, and this we see in 

 examining a cartilage near its surface (PL V. fig. II) ; 

 more frequently, however, it encloses several, but 

 rarely more than five or six (PL V. fig. I). > 



The fundamental substance of true cartilage is a 

 hard and elastic material in which no trace of struc- 

 ture can be detected. In old age, and sometimes 

 even in adult life, it becomes infiltrated with fat, and 

 often presents minute cracks which appearance has 

 been mistaken for the spontaneous generation of fibres 

 in a structureless material. But in reality they are 

 no more fibres than the granular striae of fibrine to 

 which they Bear an accurate resemblance. 



This fatty transformation, or atrophy, is often found 

 in the costal cartilages, and is recognisable by the 

 naked eye in the form of dead white or reddish yel- 

 low spots. 



Cartilage is made up exclusively of the elements 

 just described. In adult life neither nerves nor blood- 

 vessels can be recognised in it. The latter, it is true, 

 are occasionally encountered, but only during the 

 forming stage of the tissue, or where it is undergoing 

 transformation into bone, as we shall see hereafter. 

 Thus, to sum up in a word, true cartilage consists of 

 a structureless fundamental substance or basis, studded 

 with minute cavities, lined by a membrane, and en- 

 closing cells. 



Cartilages are enveloped by a membrane called 

 perichondrium. This membrane is formed by an 

 interlacement of connective fibres with delicate elastic 

 fibres, an occasional nervous fibrilla, vessels in vari- 



