164 STRUCTURE AND ENDOWMENTS OF ANIMAL TISSUES. 



highest magnifying power. They are, however, surrounded by vessels 

 (Fig. 40), which form large ampullce or varicose dilatations at their 

 edges, or spread over their surfaces ; and it is by the fluid which is 

 drawn from them by the Cartilage-cells, that the latter are nourished. 

 The nutrition of a mass of Cartilage thus seems to bear a strong resem- 

 blance to that of the thick fleshy Sea-weeds, which are in like manner 

 composed entirely of cells, with intercellular substance disposed between 

 them in greater or smaller amount. The cells in nearest proximity to 

 the nutrient fluid, draw from it the requisite materials, and transmit 

 these to the cells in the interior of the mass, receiving a fresh supply in 

 their turn from the source' in their own neighbourhood. When the Ar- 

 ticular or other cellular Cartilages are inflamed, however, we find ves- 

 sels passing into their substance ; but these vessels are formed in an 

 entirely new tissue^ which is the product of the inflammatory process, 

 and cannot be said to belong to the Cartilage itself. 



271. The temporary Cartilages, which have a like cellular structure, 

 but which are destined to undergo metamorphosis into Bone, are equally 

 destitute of vessels when their mass is small ; but if their thickness ex- 

 ceed an eighth of an inch, they are permeated by canals for the trans- 

 mission of vessels. Still these vessels do not ramify with any minute- 

 ness in the 'tissue ; and they leave large islets, in which the nutritive 

 process must take place .on the plan just described. 



272. The Fibro-Cartilages, formed as it were by the intermingling of 

 two distinct elementary structures, have a degree of vascularity propor- 

 tioned to the amount of the fibrous tissue which they contain ; but these 

 vessels do not penetrate the cellular 1 portions, where such are distinct 

 from the mixed structure. 



273. The Cartilaginous tissue appears to be more removed than 

 almost any other in the body from the general tide of nutritive action. 

 Its properties are simply of a physical character ; and they are not im- 

 paired for a long time after the death of the tissue, its tendency to de- 

 composition being very slight, so long as it is exposed to ordinary tem- 

 peratures. It is protected by its toughness and elasticity from those 

 mechanical injuries to which softer or more brittle tissues are liable ; 

 and consequently it has little need of any active power of reparation. 

 When loss of substance occurs as a result of disease or accident, this seems 

 never to be repaired by real cartilaginous substance ; but the space is 

 filled up by a fibrous tissue developed from the reparative blastema ( 213). 

 It is in this tissue that the new vessels are found, which have been erro- 

 neously supposed to penetrate the cartilage when it becomes inflamed ; 

 the fact being, that the vessels are restricted to the " false membrane" 

 formed in the inflammatory process, which takes the place of the carti- 

 laginous tissue that has disappeared in consequence of imperfect nutri- 

 tion or degeneration. 



274. The Cornea of the Eye bears a superficial resemblance to 

 Cartilage ; but it corresponds rather with Fibrous Membranes in its 

 elementary structure. Besides its anterior or conjunctival layer, which 

 consists of epithelium, and its posterior layer of cells constituting the 

 epithelium of the aqueous humour, the Cornea has been shown by Mr. 

 Bowman to consist of three layers, of which the anterior and the poste- 

 rior (which are very thin) have some of the characters of the yellow 



