THE CONNECTIVE TISSUES. 



39 



placed quadrate elements are seen in tendon, while sheets of flattened 

 endothelioid plates characterize basement-membranes and envelop 

 the bundles of fibrous tissue. 



In the denser structures the cells occupy spaces within the 

 ground-substance ; these spaces usually communicate directly with 

 one another by means of minute channels, or canaliculi, and form a 

 complicated system of "juice-canals" through the entire tissue. 

 Within these tissue -spaces, or lacuna, lie the connective-tissue 

 corpuscles, generally only partially filling the cavities, Imcf being 

 usually Especially applied to one wall of the space after the manner 

 of an endothelial covering. These interjas^icular cjejts within the 

 ground-substance may be regarded as the radicles of the lymphatic 

 system, in some localities, as in the peritoneunT, standing in close 

 relation with both the Ivmphatic and the bloodchannels. 



The intercellular of horous constituents oTconnective tissue are of 

 two kinds white fibrous and yellow elastic tissue. "White fibrous 

 tissue ordinarily occurs as wavy bundles of varying thickness, com- 

 posed of silky fibrils of such fineness that, under ordinary amplifica- 

 tion, they present no appreciable thickness ; these bundles sometimes 

 run parallel, as in tendon, but more frequently interlace, forming 

 coarser or finer mesh-works, as seen in the omentum and subcu- 

 taneous tissues. When examined after teasing, the ultimate fibrils 

 of the white fibrous 

 tissue appear as a FIG. 40. 



confused mass of 

 delicate interlacing 

 lines, but in their 

 undisturbed relation 

 they lie parallel, 

 whatever may be the 

 general disposition of 

 the bundles. Fibrous 

 tissue yields^ gela- 

 tin on boiling in 

 water, and swells up 

 and becomes in- 

 distinct on treat- 

 ment with acetic acid. 



Yellow elastic 

 tissue, on the con- 

 trary, occurs usually 

 as a net-work of dis- 

 tinct fibres lying among the bundles of the white fibrous tissue. 

 Examined in detail, the elastic fibre appears highly refracting and 





White fibrous tissue : 

 one end of the bundle has 

 been teased to display the 

 component fibrillae. 



Elastic fibres isolated ; from the ad- 

 ventitia of the aorta. (After Schief- 

 ferdecker.} 



