250 



DEVELOPMENT OF CARTILAGE. 



In the Intel-vertebral fibro-cartilages, many of the cartilage-cells are provided 

 with long and ramified processes that extend far beyond the body of the cell. 



The proportion which the fibrous bundles bear to the true cartilage, differs 

 much in different examples of this tissue. In general the fibrous tissue very greatly 

 predominates, and in some cases, as in the interarticular laminse of the knee-joint, it 



Fig. 292. WHITE FIBRO-CARTILAGE FROM AN INTERVERTEBRAL DISK (HUMAN). HIGHLY MAGNIFIED. 



(E. A. S.) 



The concentric lines around the cells indicate the limits of deposit of successive capsules. One of 

 the cells has a forked process which extends beyond the hyaline area surrounding the cell, amongst the 

 fibres of the general matrix. 



constitutes almost the entire structure, but cartilaginous tissue with characteristic 

 cells predominates near the surfaces. In the intervertebral disks the cartilage- 

 corpuscles are, as already stated, more abundant towards the central pulp than near 

 the periphery, but the centre of the pulp itself does not contain cartilage-cells, but a 

 reticulated cell-structure embedded in soft matrix, derived from the cells of the 

 chorda dorsalis of the embryo. In all the symphyses the cartilage which is in 

 immediate contiguity with the bony surfaces is hyaline. 



In the healthy state, no blood-vessels penetrate the articular cartilages. What- 

 ever nutrient fluid they require seems to be derived from the vessels of adjoining 

 textures, especially the bone, and to be conveyed through the tissue by imbibition. 

 Towards the circumference of the cartilage, however, underneath the synovial 

 membrane, the synovial vessels form a narrow vascular border round it, which has 

 been named the circulus articuli vasculosus. 



"When the tissue exists in thicker masses, as in the cartilages of the ribs, canals 

 are here and there excavated in its substance, along which vessels are conducted for 

 the nourishment of the parts too distant to receive it from the vessels of the 

 perichondrium. But these canals are few and wide apart, and the vessels do not 

 pass beyond them to ramify in the intermediate mass, which is accordingly quite 

 extravascular. Besides blood-vessels these canals usually contain a number of cells 

 resembling lymph-corpuscles, a few connective tissue corpuscles and even in places 

 some connective tissue fibres. The contents of the canals are sometimes spoken of 

 as " cartilage-marrow." The cartilage cells in the immediate neighbourhood of the 

 canals are disposed as at the surface of the cartilage, i.e., they are flattened 

 conformably to the wall of the canal. 



No nerves have been traced into any of the cartilages, and they are known to be 

 destitute of sensibility. 



The matrix of cartilage is converted after long boiling into a substance termed chondrin 

 which gelatinizes on cooling. This may be due however to its containing gelatine (see p. 245). 



DEVELOPMENT OF CAETILAGE. 



The parts of the embryo which are to become cartilages are made up at first 

 of the common mesoblastic cells from which the connective tissues generally 

 originate. After a time the cell-contents become clearer, the nucleus more visible, 

 and the- cells, mostly of polygonal outline, appear surrounded by clear lines of 



