CONNECTIVE TISSUE. 



FIG. 37. Fragment 

 of fenestrated mem- 

 brane from large ar- 

 tery ; surface view. 



elastic fibres appear as minute polygonal areas, separated by the white fibres 

 and the associated connective tissue cells. Where, on the other hand, elas- 

 ticity would be disadvantageous, as in tendons and aponeuroses, very few 

 elastic fibres are present, the dense fibrous structures being composed 

 practically of white fibres alone. Within the walls of the 

 large blood-vessels, the broad ribbon-like elastic fibres are 

 fused into membranous tracts, which contain numerous 

 openings of various size (Fig. 37) and are, therefore, 

 known as fenestrated membranes. Elastic fibres withstand 

 dilute acids and alkalies, consequently becoming more evi- 

 dent in tissue treated with acetic acid in which the white 

 fibres disappear. In their chemical composition they differ 

 from the white fibres, yielding elastin and not gelatin on 

 boiling and disappearing upon being subjected to pancre- 

 atic digestion. Likewise, in their staining reactions elastic 

 fibres differ from the white; by taking advantage of the 

 affinity which the former possess for certain dyes, as orcein, 

 a much wider and more generous distribution of elastic 

 tissue has been established than was formerly appreciated. 



Loose fibrous or areolar tissue occurs throughout the body wher- 

 ever the opposed parts although connected enjoy considerable mobility. 

 Familiar examples are the sheets or tracts of yielding connective tissue, which 

 lie between the skin and underlying fascia or beneath mucous membranes, 

 that unite the muscles and assist in keeping the viscera in place. The 

 variable bundles of white fibres are loosely and irregularly disposed, crossing 



in all directions and enclosing cor- 

 respondingly indefinite lymphatic 

 clefts. The elastic fibres form a 

 network of highly refracting threads 

 which, in sections and teased prepa- 

 rations, are more or less wavy and 

 curled. The cellular constituents of 

 the tissue are relatively inconspicu- 

 ous, but here and there the connec- 

 tive tissue cells are seen as spindle- 

 shaped or irregular plate-like bodies 

 applied to the surface of the fibrous 

 bundles. They are bathed by the 

 tissue-juices that well through the 

 interfascicular spaces within which 

 clefts are also lodged the migratory 

 lymphocytes and other forms of free 

 cells. 



Dense fibrous tissue owes 

 its characteristics to the more com- 

 pact and orderly arrangement of the 

 bundles of white fibres. Although 

 the individual fibres are no thicker 

 than in the areolar tissue, they are 

 grouped into larger bundles and held more closely together by the inter- 

 fibrillar cement or ground-substance. The bundles are disposed with greater 

 regularity, either as closely packed parallel fasciculi, as in ligaments, tendon 

 and aponeuroses, or as intimately felted bands forming fibrous sheets, as in 



FIG. 38. Portion of omentum, showing fibre-elastic 

 tissue arranged as a fenestrated membrane ; the nuclei 

 belong to the connective tissue and surface endothelial 

 cells. X 120. 



