loo chord ate anatomy 



Tissues Serving for Mechanical Support 



Protoplasm is a substance of semi-fluid or gelatinous consistenc\-. 

 An elephant constituted of protoplasm only is a mechanical impossibility. 

 Large animals, especially if they are land animals, require mechanical 

 support. Protoplasm provides such support by appropriating various 

 materials from the environment and building them into non-living struc- 

 tures which are external to the cells and physically adapted to the 

 mechanical needs of the animal as a whole and of its parts. 



The basis of the material of these supporting structures consists of 

 various nitrogenous or protein substances. By impregnation of the 







/. f \ 





\ ^ 





A B 



Fig. 96. — -.4, mesenchymal tissue from, embryo of the amphibian, Ambystoma. 

 B, pigment cells from Ambystoma; below, a cell with pigment dispersed in numerous 

 branched processes of the cell; above, a "contracted" cell with pigment concentrated, 

 the transparent processes not shown. (From Kingsley.) 



material with inorganic salts, chiefly those of calcium, hard or rigid 

 supporting structures are produced. The protoplasmic or cellular 

 agencies concerned in building the supporting tissues are mesenchyme 

 cells, except in the cases of the notochord and the ectodermal neuroglia 

 (page 99) of nervous organs. 



The embryonic precursor of supporting tissues other than the excep- 

 tions mentioned is a more or less spongy mesenchyme (Fig. 96.4) whose 

 individual cells have branching processes by means of which the cells 

 are joined together The spaces within the meshwork of cells is filled 

 by a homogeneous fluid substance, the matrix. Presumably the cells 

 are the source of the matrix. 



Connective Tissue 



The essential mechanical structures in connective tissue are relatively 

 coarse white fibers consisting of an albuminoid substance, collagen, 



