66 NORMAt HISTOLOGY AND ORGANOGRAPHY. 



are frequently found, particularly in the connective- 

 tissue elements. 



Fat in the human body is mostly found stored 

 up in modified connective-tissue cells. This may 

 occur wherever there is connective tissue, and fat 

 cells must therefore be regarded as modified connec- 

 tive-tissue cells. Likewise certain pigment cells 

 and red blood corpuscles belong to this class. 



The supporting tissue is derived exclusively from 

 the mesenchyma, a subdivision of the middle germ 

 layer or mesoderm. It is divided into three classes 



connective tissue, carti- 

 lage, and bone. 



Fig. 30. Connective-tissue cells from 

 a chick embryo. 



Fig. 31. Connective-tissue 

 cells from Wharton's jelly of 

 the umbilical cord. 



1. CONNECTIVE TISSUE. 



The elements of this tissue consist of cells and cell 

 products, in the form of connective-tissue fibers, 

 which penetrate and give consistency and support to 

 every organ in the body. 



i . Connective-tissue Cells. 



(a) Embryonic Connective-tissue Cells. These are 

 irregular, stellate cells found in embryos and in the 

 umbilical cord. Those of the cord, with the matrix in 

 which they are imbedded, form a soft, pulpy mass 



