252 



DEVELOPMENT OF CARTILAGE. 



The matrix, although thus formed of the capsules, usually becomes to all 

 appearance homogeneous ; but in sections of cartilage that have been exposed to 

 acids and other re-agents, the contour lines of the capsules round cells and cell- 

 groups may be more or less distinctly brought into view. 



The mode in which the division of the cartilage-cell takes place has been care- 

 fully studied by Schleicher, and the stages of the process followed in the living 

 tissue (fig. 294). The nuclear membrane first of all disappears, or is converted 

 into filaments of chromoplasm. These become lost amongst the other filaments 

 which result from the conversion of the nucleoli and other more solid contents 

 of the nucleus. The filaments are at first short and irregular (#), and soon take on 

 a stellate arrangement (&). After a time they become grouped in a parallel manner 

 in the centre of the nucleus (c,d). The parallel fibres soon divide into two groups, 

 which pass towards the poles of the nucleus. Sometimes the gap between the 

 groups is bridged across for awhile by fine filaments. The two groups of fibres next 

 undergo a gradual process of conversion into the daughter-nuclei (e-K). 



It will be seen, from the above account, that the division of the nucleus of the 

 cartilage cell resembles on the whole that which has been observed in other cells, 

 The mode of division of the cell-substance is, however, different from that 



Fig. 294. DIVISION OP A CAKTILAQE CELL (Schleicher). 



a-Ji, stages of division of a cell, as seen in the living cartilage of the salamander (the connection of 

 the nucleoplasmic filaments could not be made out in the fresh condition), a, b, stellate phase ; 

 c, d, commencing separation of the nucleo-plasmic filaments ; the further stages of separation are not 

 represented ; c, filaments fully separated into two groups, and a septum beginning to be formed between 

 them ; /, septum completed, seen to be double and continuous with capsules of daughter cells ; g, h, 

 further stages in the formation of the daughter nuclei. 



which obtains in most animal-cells, for in place of a constriction appearing 

 and gradually separating the protoplasm into two halves from without in, 

 a partition is formed (<?), in the middle of the now elongated cell, as is most 

 commonly the case in the division of plant-cells. The septum, as soon as it is 

 broad enough, is seen to consist of two layers, which are continuous with the 

 capsules of the two daughter-cells (/). 



In the case of elastic cartilage the matrix is at first hyaline, and the elastic 

 fibres are subsequently produced in it. They appear in the form of fine granules 

 in those parts of the matrix that are in immediate contiguity with the cartilage- 

 cells. In the cartilage of the external ear this change occurs about the fifth 

 month of intra-uterine life, commencing in the more central parts, and gradually 

 extending outwards towards the perichondrium. 



The mode of development of white fibro-cartilage has not been fully 

 ascertained, but it appears that the fibres are formed at the same time as the 

 matrix instead of subsequently as in the case of elastic cartilage. 



