100 DEVELOPMENT OF CARTILAGE AND BONE. 



according to which the growth of cartilage proceeds. I do not 

 wish to cast any doubt upon the importance of these observed 

 phenomena ; but I must guard myself strenuously against being 

 supposed to think that the growth of cartilage is provided for, 

 even in major part, by this internal multiplication of cells and 

 intercellular substance. Cartilage grows mainly by peripheric 

 apposition. The perichondrium furnishes embryonic cells, which 

 proceed to surround themselves with a layer of hyaline inter- 

 cellular substance, which becomes continuous with the matrix of 

 the existing cartilage. The oftener this process is repeated, the 

 more cells does the cartilage contain. Those cells which were 

 originally peripheric are gradully pushed towards the centre ; 

 and it is not till after this has occurred that the second factor in 

 the growth of the cartilage comes into operation, sc, the gradual 

 enlargement and subsequent division of the individual cells as 

 they advance towards the centre of the mass. During this cen- 

 tripetal movement each element divides from one to three times. 

 The division always occurs at the thickest part of the cell, in a 

 plane at right angles to its long axis ; hence the highly charac- 

 teristic forms of the daughter-cells and their progeny. Half 

 and quarter spheres, cones, &c., retain their peculiar shape 

 throughout life, owing to the density of the matrix; for the 

 same reason the cells which result from fission are never far 

 apart, so that in the cartilages of an old man of ninety we ma}- still 

 observe those appearances which, when we saw them in young 

 cartilage, led us to attach so high an importance to the internal 

 growth of the tissue ; in either case moreover we can determine 

 with equal certainty whether the original cartilage-cell under- 

 went fission once, twice, or three times, before assuming the 

 final attitude of its repose. 



Quite independent of the phenomena of normal growth, 

 is a peculiar metamorphosis of hyaline cartilage, which we 

 find (apart from morbid states) wherever the cartilage ad- 

 joins a growing bone. Whether the cartilage takes any active 

 part in the development of bone, whether cartilage-cells, or even 

 descendants of cartilage-cells, can be converted into marrow- 

 cells or bone-corpuscles is still an open question. The metamor- 

 phosis now under consideration must however be regarded 

 as a passive participation of the cartilage, in so far as it re- 

 places the unyielding hyaline substance by a soft material,., 



