ANIMAL TISSUES. 



373 



tions is termed chondiine ; the cells of which become consolidated by 

 calcareous deposits, and a gradual transition results therefrom. Car- 

 tilage is the firmest structure next to bone ; it is very elastic, and 

 is converted by the intercellular substance into two kinds. In a rib 

 we find that this substance is uniform, and has a bluish appearance, or 

 is slightly granulous ; this is termed true, or white cartilage. The 

 other form of intercellular substance is developed in fibrous substances ; 

 and in this peculiarly-formed felt-work, cells and nuclei are imbedded. 

 It is termed yellow, fibrous, or spongy cartilage ; the yellow colour 

 depends on the mode of fibrous arrangement of the intercellular sub- 

 stance : it is found in the ear, <fcc. 



Cartilage forms the entire skeleton in some kinds of fishes, as the 

 skate, lamprey, (fee. It is nourished without coming into direct con- 

 tact with the blood-vessels, and is therefore said to be non-vascular, 

 deriving nourishment by imbibition from the surrounding blood-vessels. 

 When examined microscopically, the simplest form of cartilage is found 

 to resemble in a striking manner the cellular tissue of vegetables ; it 

 consists of an aggregation of cells of a spherical or oval figure, capable 

 in some cases of being separated from each other, but every cell having 

 a nucleus, with a nucleolus in its interior. In figs. 176 and 177 we have 

 given varieties of this structure. In the more' highly advanced scale 

 of animals a strong fibrous capsule or sheath surrounds the cartilage- 

 cells, and some of the fibres dip in amongst the cells, and bind them 

 firmly together. In those of the Eay and Shark kind, where the entire 



.3 2 



fig. 176. 

 1. CartUage from ear of mouse, resembling a section of vegetable tissue, with several 

 superimposed layers. 2. Cartilage from rabbit's ear, stowing large cells imbedded 

 in a fibrous matrix. 3. Cartilage from human ribs, with cells in groups, each 

 having a granular nucleus : magnified 200 diameters, 



skeleton is cartilaginous, the cell is imbedded in a matrix, which may 



