OF CARTILAGE. 



also accord with the young colls of plants. Compare plate I, 

 fig. 8, ff, with fig. 2. The form of the nucleus likewise corre- 

 sponds with that of many vegetable cells. In these young cells 

 of cartilage, it is presented to the observer as a small oval or 

 perfectly spherical corpuscle, having, in many instances, a 

 granulous and somewhat yellowish appearance, and containing 

 one or two nucleoli. (Compare this with the description of the 

 nucleus of vegetable cells in the Introduction.) The nucleus of 

 the cartilage-cell appears to be hollow, a fact which has not 

 been observed with regard to the cytoblast of vegetable cells, 1 

 and the nucleoli lie close upon, or in the neighbourhood of the 

 internal surface of its wall, whilst, according to Schleiden, thc\ 

 lie deep in the cytoblast of vegetable cells. 



The cartilage-cells, when once formed, appear to be endued 

 with the capacity to grow throughout the entire mass of the 

 structure. The case is different with regard to the formation 

 of new cells. This takes place in certain situations only, on 

 the surface of the cartilage, for instance, or between the last 

 formed cells. We have alread}^ seen that in the branchial rays 

 of fishes, the least developed cells lay at the point, and 

 lateral margins. The little rod, which the branchial ra\ 

 represents, does not increase in size by the formation of new 

 cells between the original ones throughout its entire length, 

 but its extension in the longitudinal direction is produced 

 by the development of new cells in the neighbourhood of 

 the point, and it increases in breadth by the same process 

 going on in the neighbourhood of the side Avails. It is a 

 familiar fact, that the cylindrical bones grow chiefly upon the 

 surface and at the end of the shaft. The formation of new 

 cartilage-cells usually takes place only in the neighbourhood of 

 the surface which is in contact with the organized substance, 

 (I refer throughout this passage to that period alone, at which 

 the cartilage docs not contain any vessels of its own,) but it 

 is not exclusively confined to that situation, it may also 

 proceed in the intercellular substance between the last-formed 

 cells. 



At the period of ossification, the earthy matter is first de- 

 posited in the cell-walls, or in the true cartilage-substance, the 



1 In a letter which I have received from Schleiden, he informs me t lint lie has 



also found hollow nuclei in plants. 



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