CARTILAGES. 285 



Nuclei. The nuclei contained in cartilage cells are mostly 

 granular, but sometimes present a smooth aspect, and then 

 are scarcely to be discriminated from particles of oil or fat : 

 in form they are sometimes rounded, but in general they are 

 irregular in shape, and follow more or less closely the contour 

 of the cells in which they are enclosed ; they also frequently 

 enclose a nucleolus. 



Usually but a single nucleus is contained in each cell ; 

 occasionally, however, two, three, and even several are in- 

 cluded within it ; and sometimes it happens that one or more 

 of these is invested by a distinct cell membrane. (See Plate 

 XXXI) 



The cells also include, as already remarked, particles of oil 

 of a globular form and of a shining aspect : it has been sug- 

 gested that these may probably in some cases be transformed 

 nuclei. 



The distinction of cartilages into true and fibro-cartilages, 

 although useful for the purposes of classification, is to some 

 extent artificial, since, on the one hand, some of the true 

 cartilages, as old age approaches, become converted into fibro- 

 cartilage, and on the other, the fibro-cartilages themselves, in 

 the early period of their development, do not contain fibres, 

 the cellular substance being hyaline, and identical with that 

 of true cartilages. 



The conversion of hyaline cartilage into fibro-cartilage has 

 been observed to occur only in those cartilages which are 

 subject to become ossified, as those of the ribs, the thyroid, &c. 



Where ligaments are inserted into true cartilaginous tissue, 

 this in the neighbourhood of such insertion always exhibits a 

 fibrous structure, in consequence of the fibres of the ligament 

 penetrating into the intercellular substance. These fibres 

 are of a nature totally distinct from proper cartilage fibres, as 

 will be seen hereafter. 



FIBRO-CARTILAGES. 



Fibro-cartilages differ chiefly from true or hyaline car- 

 tilages, in that the homogeneous intercellular substance is 



A A 4 



