TISSUES, ORGAN'S, AND SYSTEMS. 59 



particularly to be noted, as by these properties it is fitted for 

 its various uses. In growing cartihiges the change of 

 material is very energetic; they constantly contain, in certain 

 localities, numerous blood-vessels in peculiar canals; and, as 1 

 have demonstrated in the nasal cartilage of the calf, even nerves. 

 Their growth takes place, firstly, by endogenous multiplication 

 of cells, traces of which are always clearly to be observed in 

 perfect cartilages ; and secondly, by the deposition between 

 the cells, which originally exist alone in all cartilages, of 

 an interstitial substance from the blood plasma, which, accord- 

 ing to Schwann, at first yields no chondrin even in the 

 true cartilages, and subsequently gradually increases in quan- 

 tity. In perfect cartilages the nutrition is by no means 

 energetic; and it has, apart from the vessels of the peri- 

 chondrium which invests many cartilages, and those of the 

 neighbouring bone, no particular agent, except in the cartilages 

 (septum of the nose) of a few mammalia, and in the 

 plagiostome fishes, in some of which last, according to Leydig, 

 even in old individuals, vascular canals exist (Raja), in others 

 anastomosing, fusiform, or stellate corpuscles (Sharks). With 

 age, the intermediate substance of certain true cartilages readily 

 becomes fibrous, and very similar in its chemical characters to 

 that of the reticulated cartilages, which demonstrates that 

 these two kinds of cartilage are not widely separated ; the true 

 cartilages also not uncommonly ossify, vessels, cartilage, and 

 medulla being formed in them at the same time. Cartilage 

 possesses no power of regeneration, nor do _ 19 



wounds in cartilage unite by cartilage ; on the £ 



other hand, an adventitious development of 

 cartilage is not uncommon. 



The different kinds of cartilage are : 



a. Cartilage without interstitial substance, or 

 parenchymatous cartilage. To this belong 

 the chorda dorsalis of the embryo and of many 

 adult fish ; many foetal cartilages ; the carti- 

 lages of the gill lamina? of fishes in part ; and 

 those of the external ear of many mammalia. 



b. Cartilage with interstitial substance. 



Fig. 19. Portion of the chorda dorsalis of an embryo sheep, 6'" long: a, sheath 

 b, cells, with clear vesicular spaces. 



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