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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Fig. 42. 



Fig. 4;j. 



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 iind 

 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, clastic fibres are 

 found; if present in great number, these idiangc the bluish shinv, 

 Injalhic cartilage into the yellow-colored das/ic cartilage. 



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

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



