74 



NORMAL HISTOLOGY. 



usually run a sinuous course. At intervals they divide, and the 

 branches anastomose with each other to form a fibrous network, the 

 meshes of which may be large, as is the case in areolar tissue, or so 

 small and bounded by such broad fibres that the network resembles 

 a membrane pierced by somewhat elongated apertures, as is exem- 

 plified in the fenestrated membranes of the arteries. The forma- 

 tion of such a network is, however, not an essential characteristic 

 of these fibres, for they appear as isolated wavy fibres in some of 

 the fibrous tissues of open and loose structures. Elastic fibres are 

 not affected by acetic acid, nor do they yield gelatin on boiling in 

 water. According to Schwalbe, they have a tubular structure, con- 

 sisting of a membrane enclosing a substance called " elastin." 



We may now turn our attention to the different varieties of the 

 fibrous tissues. 



FIG. 60. 



Mucous tissue. (Ranvier.) a, stellate cells with long and branching processes; 6, elastic fibres 

 in the homogeneous, mucoid, intercellular substance, which is not visible under the 

 microscope unless artificially colored. Three of the cells are represented in cross-section. 



1. Mucous Tissue (Fig. 60). The cells of this elementary tissue 

 are chiefly of the third variety mentioned above. They are spindle- 

 shaped or stellate in form, and many of them possess processes 

 that extend far into the intercellular substance, where they may 

 branch and unite with the processes of neighboring cells. The 

 predominant constituent of the intercellular substance is a gelatinous 

 ground-substance, which contains a variable amount of mucin and 

 appears nearly, if not quite, homogeneous under the microscope. 

 It is this which gives the whole tissue its soft and gelatinous con- 

 sistency. A variable number of fibres of both the kinds already 

 described run through this ground-substance. The white fibres are 



