282 THE TISSUES. 



ficial form a dark band of considerable breadth around its margin. 

 Opacity very frequently results from the organization of plasma in 

 the tubular interspaces, and between the laminas ; the new forma- 

 tion not being transparent like the original tissue. 



The arcus senilis, occurring mostly in aged persons, results from 

 a fatty degeneration of the cornea. 



Distribution of White Fibrous Tissue in the Lower Animals. 



This tissue is found in all vertebrate animals in about the same 

 conditions as in man; while in the invertebrata it is very rare. In 

 rnollusca the tendinous fibres are very large; in the terebratula, 

 even -g^ of an inch in diameter, and collected into strong bundles 

 presenting a beautiful silvery aspect. In birds, the tendons of the 

 legs are very large, and more or less ossified. Every one has 

 noticed this, especially in the case of the turkey, goose, and other 

 species most frequently used as food. The analogy of this tissue 

 to bone, in a chemical point of view, has already been suggested 

 (p. 276), and will account for its tendency to ossification. 



Development of White Fibrous Tissue. 



Bonders and Virchow coincide in the opinion that the true white 

 fibrous tissue (the gelatinous intercellular tissue of white fibrous 

 tissue, bones, and teeth), does not originate from cells, but is directly 

 separated from a plastic fluid ; while the other elements lacuna 

 and pores, cartilage-cells, and nuclear (elastic) fibres are primarily 

 formed from cells. Kolliker thinks differently as to the develop- 

 ment of the fibres of white fibrous tissue ; asserting that the nuclear 

 fibres are developed not from the nuclei of the cells of the white 

 fibrous tissue of the embryo, but from the cell- walls; while the 

 cell-contents are converted into the collagenous element, or white 

 fibrous tissue. 



We agree with Eeichert and Virchow that the elastic fibres 

 blended with the collagenous element, or true white fibrous tissue, 

 represent the cells of cartilage; while the white fibrous tissue re- 

 presents the matrix or homogeneous substance of cartilage; and, 

 like the latter, is not developed from cells. This view is confirmed 

 by an examination of the insertion of tendons into bones in young 

 animals, and in which the surface of the latter is still in a state of 

 cartilage. 



The white fibrous tissue alone has been confounded with the 

 areolar, under the name of the connective tissue. Kolliker's " areo- 

 lated connective tissue" is the true areolar tissue, and will be de- 



