CELLULAR DIFFERENTIATION 



55 



fibrous ; it may be almost wholly organic, or very largely inor- 

 ganic. The principal classes are cellular connective tissues, ge- 

 latinous connective tissue, fibrous connective tissue, cartilaginous 

 tissue, and osseous tissue. 



Fig. 23. 



Pig. 23. Gelatinous connective tissue, showing stellate cells (c), epithelium (jc), the gelatinous 

 intercellular substance (5), and the intercellular fibres (/). 



Questions on the figure. — What seems to be the relation of the epithelial layer 

 to the tissue below it? What classes of cells are found in the gelatinous tissue? 

 What is their origin? What is the nature of the intercellular substance? Are the 

 fibres cellular or intercellular? 



74. Cellular or Vesictilar Tissue forms an exception to the general rule of abun- 

 dant intercellular substance. It is an embryonic tissue, — a forerunner of the more 

 permanent tissues, — and is chiefly interesting from that fact. The cells have 

 large vacuoles or vesicles which are enveloped by a thin layer of protoplasm (Fig 

 22). It is found in the notochord of vertebrates. 



75. Gelatinous tissue has a matrix of intercellular substance enveloping stellate 

 cells, the radiating projections of which serve to connect them. Fibres are often 

 developed in the matrix. This tissue is abundantly found in the jelly-fish (see 

 Fig. 23). 



76. Fibrous connective tissue has in its ground substance a rich supply of 

 fibrils variously arranged. The cells or corpuscles are often elongated and 

 branched. If the 'intercellular fibres cross, running in various directions, a loose 

 yielding tissue results, as in the ordinary connective tissue about the muscles and 

 nerves (Fig. 24, ^); if the fibres are parallel the tissue naturally becomes more 

 compact. There are two types of the more compact sort differing in the quality 

 of the fibres. The latter may be white and inelastic, as in tendons, or yellow and 

 elastic. Fat is frequently deposited as spherical drops of oil'(Fig. 24, B) in the cells 

 of connective tissue. 



77. Cartilage. — In cartilage the intercellular matrix is much firmer than in 

 those tissues already described. It may appear homogeneous as in rib cartilage 



