CARTILAGE. 



723 



Cellular Cartilage of Mouse's-ear. 



have an example of a tissue essentially composed of Cells ; but 

 these are commonly separated from each other by an ' Intercellular 

 substance,' which is so closely adherent to the outer walls of the 

 cells as not to be separable from them (§ 539). The thickness of 

 this substance differs greatly in different kinds of Cartilage, and 

 even in different stages of the growth of any one. Thus in the 

 Cartilage of the external Ear of a Bat or Mouse (Fig. 384), the 

 cells are packed as closely 



together as are those of an Fig. 384. 



ordinary Vegetable paren- 

 chyma (Fig. 198, a) ; and 

 this seems to be the early 

 condition of most Cartilages 

 that are afterwards to pre- 

 sent a different aspect. In 

 the ordinary Cartilages, how- 

 ever, that cover the extre- 

 mities of the bones, so as 

 to form smooth surfaces for 

 the working of the joints, the 

 amount of Intercellular sub- 

 stance is usually considerable ; and the cartilage-cells are com- 

 monly found imbedded in this, in clusters of two, three, or four 

 (Fig. 385), which are evidently formed by a process of 'binary 

 subdivision ' ana- 

 logous to that by y IG- 355. 

 which the multi- 

 plication of cells 

 take place in the 

 Vegetable King- 

 dom (§ 185). The 

 substance of these 

 cellular Carti- 

 lages is entirely 

 destitute of Blood- 

 vessels ; being 

 nourished solely 

 by imbibition 

 from the blood 

 brought to the 

 membrane cover- 

 ing their surface. 



Hence they may Section of the branchial Cartilage of Tadpole :— 

 be compared, in a> group of four cells, separating from each other ; 

 regard to their b, pair of cells in apposition ; c, c, nuclei of carti- 

 <*rade of organiza- l a g e " cells > d > cavity containing three cells. 

 tion, with the 



larger Algae ; which consist, like them, of aggregations of cells held 



3 a 2 





