GENERAL HISTOLOGY 



75 



distinctions between the various kinds rest chiefly upon the differences 

 of this intercellular substance. The following forms are distinguished: 

 (i) cellular connective tissue; (2) homogeijeous connccdve tissue; (3) 

 fibrous connective dssue; (4) cartilage; (5) bone. 



Cellular Connective Tissue (which, strictly speaking, does not 

 belong here, since it does not arise from mesenchyme but directly from the 

 metamorphosis of epithelium) shows the characteristics of the group least 

 disdncdy. It owes its name to the fact that the cells make up the chief 



Fig. 39. — Cellular connective sub- 

 stance. Cross-section through the 

 notochord of a newly hatched trout. 



Fig. 40. — Hornogeneous connective sub- 

 stance of Sycandra raphanus (after F. E. 

 Schulze). 



mass, while the cell-products are inconsiderable. The ceUs are large, 

 vesicular bodies which are closely pressed together and are consequently 

 polygonal (fig. 39). They have between them a firm but thin layer of 

 intercellular substance. 



Homogeneous Connective Tissue. — In homogeneous connective 

 substance the intercellular substance (or matrix) is usually present in 

 considerable quantity as a transparent mass, sometimes soft like jelly, 

 often firmer (fig. 40). The cells lying in it are either spherical or send 

 branching processes into the matrix. Such processes may unite to form 

 meshes which, like a pseudopodial network, unite cell to cell. Frequently 

 the matrix contains, in addition, isolated firm fibres or threads, which, on 

 account of their physical characteristics, are called elastic fibres, and 

 consist of a substance (clastin) exceedingly resistant to all reagents. 

 Finally, in the matrix there may develop the finer connective-tissue filjrils 

 characteristic of the next group; they may become so increased in 

 number as to determine the character of the tissue. 



Fibrous Connective Tissue is characterized by the rich supply of 

 connective- tissue fibrilte; these are fibres of extraordinary fineness, lying 

 in a homogeneous matrix, which is the less evident the richer it is in 



