CONNECTIVE TISSUE. 47 



Connective Tissue. 



Connective tissue is distributed everywhere throughout the 

 body beneath the outer epithelial layer. It forms a support- 

 ing and connecting framework for the parts of the organism, 

 and to this end it envelops and penetrates all the interior 

 organs and structures. It permeates the organism so com- 

 pletely that if all the other tissues were removed the connec- 

 tive-tissue framework would still form a complete mould of 

 the body and its organs. It originates from the mesoblast, 

 except the neuroglia of the nerve-centres, which is epiblastic. 

 Like other tissues, it is made up of cells and non-cellular 

 elements, but is peculiar in that the non-cellular portions 

 largely predominate, as naturally follows from their constitut- 

 ing the main framework of the body. 



The connective-tissue cells, while differing in various situa- 

 tions, have a fundamental morphological and genetic simi- 

 larity. 



The extracellular elements serve mechanical purposes, and 

 are not endowed with vitality ; they are produced by the 

 connective-tissue cells. The most specialized and generally 

 distributed of the extracellular elements are certain fibres, 

 which are of two kinds, white fibres and yellow elastic fibres. 

 Other intercellular materials are an interstitial mucinous or 

 gelatinous substance especially found in young connective 

 tissues (as mucous tissue), the matrix of hyaline cartilage, 

 and the mineral matter in bone. 



Connective -tissue cells are of one general type, though 

 varying much in different situations. The forms associated 

 with fibrous tissues are sometimes called "fibroblasts." 

 Connective-tissue cells are sometimes round or spherical, 

 small and prominently nucleated ; such cells occur only in 

 young, growing, or embryonal forms of connective tissues. 



The mucous cell is another form of young or embryonal 

 connective-tissue cell ; it is a fiat nucleated cell of irregular 

 stellate shape, with its pointed processes, three or four in 

 number, prolonged into fine filaments which anastomose with 

 similar processes from neighboring cells. 



In some situations, especially in fibrous tissues, the connec- 

 tive-tissue cells are fusiform in shape ; in some they are 

 stellate ; in others, as in basement-membranes and the cells 



