^ OF NON-VASCULAR ANIMAL TISSUES. 165 



physal and the articular cartilage are formed and developed without the presence of 

 vessels. 



I think it may be naturally deduced from the facts demonstrated in the foregoing 

 dissections, — 



First. That during the most early periods of foetal life, the growth of cartilage 

 takes place, and that its component cells or corpuscles undergo certain progressive 

 changes in their form and size, without the presence in its substance of any blood- 

 vessels. 



Secondly. That the vessels encircling the cartilage contribute to effect such changes 

 in its corpuscles, and that the changes are facilitated by the softness of the substance 

 of the cartilage. 



Thirdly. That at the more early period of foetal development the synovial surface 

 of cartilage does not contain blood-vessels. 



B. T'he Second Stage of Development of Articular Cartilage. 



In the stage of development described in the preceding section, vessels are only pre- 

 sent in the vicinity of the articular extremities of bones, but as the cartilage forming 

 the latter becomes harder in its consistence during the subsequent periods of its 

 development, vessels are gradually introduced upon its surface and into its sub- 

 stance. 



Those epiphysal vessels which are subservient to the nutrition of the substance of 

 articular cartilage, will be first treated of, and subsequently those which belong to its 

 free or synovial surface. 



The articular arteries in the adult subject, which are so numerous, and which sur- 

 round so completely the various articulations, terminate by entering the substance 

 of the extremity of the bones, by passing between the articular cartilage and the 

 synovial membrane, and by supplying the latter membrane and the ligaments. 

 In the stage of development which is about to be described, the ends of the bones 

 are not yet ossified ; the cartilaginous epiphysal extremities of the bones will there- 

 fore be spoken of. 



First, the manner in which the branches from the articular arteries gain the in- 

 terior of the epiphysal cartilage, and their mode of distribution in the subsequent 

 periods of their development, will be demonstrated. 



Secondly, the vessels which are situated between the cartilage and the synovial 

 membrane, and which nourish the free surface of the former, will be described. 



Of the Blood-vessels in the substance of the Epiphysal Cartilage. — The whole inferior 

 extremity of the os femoris of a foetus of about five months presents, except at its arti- 

 cular surface, numerous depressions of various depths. The deepest may be regarded 

 as canals, some of which are single, others bifid ; they terminate in blind sacs. The 

 direction of some of these canals is towards the centre of the epiphysis, of others 

 towards its point of attachment to the osseous shaft, and of others, those about to 



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