OF NON-VASCULAR ANIMAL TISSUES. 173 



which, in childhood and during adult age, owing to the functions of the joints, they are 

 necessarily absent. At the period when the child begins to use the various joints, 

 and subjects them to pressure, these vessels recede ; and in adult life they are only 

 found on that margin of articular cartilage which is exempt from the influence of 

 external forces*. The arteries which pass between the articular cartilage and the 

 synovial membrane, like those of the foetus, may be considered as the termination of 

 the articular arteries. At the point where the reflexed becomes continuous with the 

 articular synovial membrane, it contains large vessels subjacent to it, which are 

 numerous and plexiform. Immediately, however, that they enter the cellular web, 

 between the articular cartilage and synovial membrane, they become enlarged and 

 straight, and pass to a greater or less distance over the border of the articular car- 

 tilage, forming loops frequently with considerable dilatations, and becoming finally 

 continuous with the veins. The free surface of adult articular cartilage appears to 

 be nourished by the liquor sanguinis, which exudes from these looped and dilated 

 vessels. 



The following are the leading facts which the preceding researches upon Articular 

 Cartilage tend to establish : — 



1. Epiphysal and articular cartilage are developed and nourished in the early 

 periods of foetal existence, without the presence of blood-vessels in the substance of 

 the former, or on the surface of the latter. 



2. At subsequent periods, canals are formed in the epiphysal cartilage, vessels are 

 prolonged into them, which converge towards the articular cartilage ; and also 

 vessels extend over a considerable portion of the free surface of articular cartilage. 



3. At later periods, the epiphysal cartilage ossifies, and for a considerable time 

 vessels are placed between the ossified nucleus and the articular cartilage. 



4. As age advances, the osseous nucleus increases in size, the blood-vessels disap- 

 pear from the cartilage which remains unossified, but the nucleus contains large and 

 numerous blood-vessels. 



5. Corresponding with the changes just noticed, is the recession of the blood- 

 vessels from the whole of that surface of the articular cartilage which is subject to 

 compression. 



6. In adult life, the articular cartilage contains no blood-vessels ; but in the can- 

 celli of the bone at its attached surface, are numerous large vessels, from which the 

 cartilage is separated by a delicate lamella of bone ; the circumference of its free 

 surface presents numerous dilated blood-vessels. 



7. Articular cartilage during the whole of life gradually becomes thinner, by being 

 converted into bone. 



* I shall take another opportunity of discussing the pathological conditions in which, in the adult subject, 

 these vessels extend over nearly the whole of the surface of the articular cartilage ; artificial injections of them 

 may be seen in most pathological museums. 



2 a2 



