HISTOLOGY 



151 



The basis of the material of these supporting structures consists of 

 various nitrogenous or protein substances. By impregnation of the mate- 

 rial 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 pecuHar connective tissue of nervous organs, 

 the neuroglia (page 149) which is ectodermal. 



The embryonic precursor of supporting tissues other than the excep- 

 tions mentioned is a more or less spongy mesenchyme (Figs. 69 and 113^) 

 whose individual cells have branching processes by means of which the 



^-^7^ 



-^.S-" 



v 



%% 



Tk 



5 ^ 



■ -■■■r'f 



A 



A B 



Fig. 113. — A, 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. C, part of a tendon in longitudinal section, highly 

 magnified; nucleated cells are seen among the tendon fibers. (From Kingsley.) 



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. 



CoNNECTrv'E Tissue 



Connective tissue consists essentially of fibers. The source of the 

 fibers has long been a matter of controversy. The earlier behef that they 

 are formed in the protoplasm of cells has largely given way in view of much 

 evidence that they arise in the intercellular matrix by some process 

 resembling precipitation, the cells probably serving merely to bring about 

 the reaction in the matrix. 



The ordinary connective tissue which is present throughout the body 

 of a vertebrate serves to bind structures together or to ensheath them, 

 provides internal support for massive soft structures or, in general, affords 



