416 



MOVEMENTS 



aorta (Piersoi, 



seen isolated that is, never arranged in bundles usually with a dark 

 double contour, branching, brittle, and when broken, their extremities 

 curled and presenting a sharp fracture like a piece of India rubber. 



These fibres take a wavy course between the 

 bundles of inelastic fibres in the areolar tissue 

 and in most of the ordinary fibrous mem- 

 branes. They are found in greater or less 

 abundance in the situations just mentioned ; 

 in the ligaments, but not the tendons ; in the 

 layers of non-striated muscular tissue ; the true 

 skin ; the true vocal chords ; the trachea, 

 bronchial tubes, and largely in the parenchyma 

 of the lungs ; the external layer of the large 

 arteries ; and, in brief, in nearly all situations 

 in which ordinary connective tissue exists. 



The second variety of elastic tissue is 

 composed of fibres, larger than the first, 

 ribbon-shaped, with well-defined outlines, anas- 

 after Schieffer- tomosing, undulating or curved in the form of 

 the letter S, presenting curled ends and sharp 

 fracture, like the smaller fibres. These measure -5 oVo to "ToVo f an mCQ 

 (5 to 8 p) in diameter. Their type is found in the ligamenta subflava 

 and the ligamentum nuchae. They are also found in some of the liga- 

 ments of the larynx, the stylo-hyoid ligament and the 

 suspensory ligament of the penis. 



The third variety of elastic tissue is found forming 

 the middle coat of the large arteries and has already 

 been described in connection with the vascular sys- 

 tem. The fibres are large and flat, inosculating freely 

 with each other by short communicating branches. 

 These anastomosing fibres, forming the so-called fe- 

 nestrated membranes, are arranged in layers, and the 

 structure is sometimes called the lamellar elastic tissue. 

 The physical property of elasticity plays an impor- 

 tant part in many of the animal functions. Examples 

 of this are in the action of the large arteries in the 

 circulation and in the resiliency of the parenchyma of 

 the lungs. The ligamenta subflava and the ligamentum nuchae are 

 important in aiding to maintain the erect posture of the body and head 

 and to restore this position when flexion has been produced by muscular 

 action. Still, the contraction of muscles also is necessary to keep the 

 body in a vertical position. 



Fig. 83. Portion 

 of the elastic tissue of 

 the intima of the human 

 aorta ; the fibres are so 

 broad and so closely 

 grouped that they con- 

 stitute an elastic sheet 

 the so-called fenes- 

 trated membrane of 

 Henle (Piersoi). 



