86 



THE TISSUES 



Two similar theories exist as to ihe development of elastic fibres, a cellular 

 theory and an extracellular theory. As in the case of the white fibrils the weight 

 of evidence points to their development in the ectoplasm, apparently in much the 

 same manner as the white fibrils. 



Classificalion:- 



Tissue 



Cartilage Fibrous 

 [ Elastic 

 Bone 



r (i) Embryonal 



Connective Tissue • 

 Proper 



Connective J | Ilyalin 



(2) Fibrillar 



(3) Elastic 



(4) Reticular 



f (a) loose or areolar 



(fat tissue, pigment- 

 ed tissue) 

 {b) formed (tendon 

 and aponeurosis) 



CONNECTIVE TISSUE PROPER 



EMBRYONAL CONNECTIVE TISSUE 



This is the least differentiated of the connective tissues and has 

 been already partly described (p. 85). It is not found in the normal 

 human adult but is described on account of its important develop- 

 mental relations to the mature forms. It is also of interest from the 

 standpoint of pathology as it is the type of connective tissue found in 

 certain new growths, and also occurs during connective-tissue repair 

 after injuries. Its structure varies considerably for different 

 developmental stages. The younger forms are little more than 

 mesenchyme with irregular stellate branching and anastomosing 

 cells scattered through an apparently structureless or slightly fibril- 

 lated semifluid ground substance. Older forms contain more dis- 

 tinct fibres of both white and elastic varieties. To a somewhat 

 more differentiated embryonal tissue in which the ground substance 

 is rich in mucin, the name mucous tissue has been given (Fig. 30). 

 It consists of a mucin-containing ground substance in which are small 

 bundles of fine white fibrils and irregular branching cells. It occurs 

 as Wharton's jelly in the umbilical cord. By some the vitreous of 

 the eye is classed as mucous tissue. It contains only a few cells and 

 only slight traces of a reticular fibrillation. 



FIBRILLAR CONNECTIVE TISSUE 



Fibrillar connective tissue, also known as white fibrous tissue, and 

 itself sometimes called connective tissue proper, consists of cells and 

 fibres lying in a basement or ground substance. The elements of 

 fibrillar tissue mav be classified as follows: 



