270 



THE TISSUES. 



The elastic fibres are arranged in three principal forms in the 

 various organs: 1, wide-meshed or intricately formed nets with 

 hook-like indentations, and forming considerable masses; 2, as 



Fig. 171. 



Fig. 172. 



Fig. 171. Elastic network from the tunica media of the pulmonary artery of a horse, with cavities 

 in the fibres. Magnified 350 diameters. (KUlliker.) 



Fig. 172. Yellow fibrous element of the areolar tissue of serous membrane, from the mesentery of 

 the rabbit, treated with acetic acid. (Magnified 300 diameters.) 



bundles of fibres nearly parallel (as in certain ligaments), or twining 

 around other tissues in a spiral manner; 3, forming a fenestrated 

 membrane with tolerably large intervals, as in the arteries. 



When the yellow elastic fibres form masses, as in the ligamentum 

 nuchse, &c., no nerves or lymphatics are found among them. The 

 vessels, comparatively few in number, lie between the fibres and 

 parallel to them, much like those of tendon. (Fig. 170, D.) The 

 connecting branches, however, are not transverse, but pass off at 

 angles of about 40 ; so that the spaces inclosed by the vessels have 

 a somewhat rhomboidal outline. 



Chemical Composition of Elastic Tissue. 



The investigations of chemists have not yet led to any very ac- 

 curate knowledge of the composition of this tissue, and its general 

 chemical relations. 



Cold acetic acid does not act upon it ; and therefore displays it 

 when blended with white fibrous tissue, by dissolving the latter, and 

 thus isolating the former. Mulder and Dundas found the fibres 

 entirely unchanged after boiling forty hours, and obtained no gela- 



