TISSUES. 36 



J 



Connective tissue {connectlvum) must be reo-aixled as 

 tonning, in order of phylogenetic age, the second main 

 group of tissues. This is morphologically characterized by 

 the intercellular substance, which develops between the 



Fig. 291. — .Telly-like tissue from the vitreous body of an embryo of four 

 nionths (round colls as jelly-like intercellular substance). 



Fig. 292. — Cartilage-tissue of the fibrous or netted cartilage of the ear- 

 shell : a, cells ; b, intercellular mass ; c, fibres in the latter. (After Frey. ) 



cells, pli^'siologically, by the double part which it plays, 

 as connecting substance and as complementary substance 

 between the other tissues, as an inner supporting substance 

 and as a protective covering for the inner organs. Of the 

 numerous forms and varieties of connective tissue, we regard 

 the jelly-like tissue (Fig. 291 ; Fig. G, vol. i. p. 126), the fatty 

 tissue, and the chorda tissue as the earlier ; the fibrous, 

 cartilaginous (Fig. 292), and bone-tissue (Fig. 0, vol. i. p. 120) 

 as the more recent formations. All these various forms of 

 connective tissue are products of the middle germ-layer, 

 or mesoderm ; or, more accurately, of the two fibrous layers, 

 of which the skin-filjrous layer is originally derived from 

 the exoderm, the intestinal-fibrous layer from the entoderm. 

 The nerve-muscular ti.ssue (nearo-musculum) is of much 

 more recent origin than the connective tissue. If epithelial 

 ti.ssue represents a primary period in tribal history, and 



