86 



GENERAL PRINCIPLES OF ZOOLOGY. 



supplant the ordinary connective-tissue fibrils and become the 

 predominant element of the connective tissue, which is then, 

 spoken of as elastic tissue. 



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1 



FIG. 43. 



FIG. 42. 



FIG. 42. Tendinous tissue. (After Gegenbaur.) 



FIG. 43. Cartilage. (After Gegenbaur.) c, perichondrium ; b, transition into typical 

 cartilage (a). 



Cartilage. Cartilage and bone are likewise tissues which find 

 their characteristic development only in the vertebrates. In its 

 appearance cartilage is similar to the homogeneous connective 

 substance of many invertebrated animals; the matrix is homo- 

 geneous and, at first glance, appears quite structureless (fig. 43), 

 but, under the action of certain reagents, assumes a fibrous condi- 

 tion. This conduct, as well as the fact that the cartilage grows 

 through changes of the perichondrium, a thin, fibrillar skin 

 covering its surface, makes it more certainly evident that it is 

 homogeneously fibrillar; and it is thereby distinguished from 

 homogeneous connective substance since it is not, like the latter, 

 .a lower but a higher stage of tissue formation. It is worthy of 

 note that the matrix of cartilage (chondrin) by cooking produces 

 a kind of glue which differs from true or glutin glue in that it is 

 precipitated by acetic acid. In the matrix the cartilage cells lie 

 united in groups and nests, a mode of grouping pointing to their 

 origin, since each group of cells has arisen from a single mother- 

 cell by successive divisions. In cartilage also, elastic fibres are 

 found; if present in great number, these change the bluish shiny, 

 hyaline cartilage into the yellow-colored elastic cartilage. 



Bone is the most complicated structure in the series of connec- 

 tive tissues. It consists of a matrix (ossein), closely allied to 



