MOVEMENTS DUE TO ELASTICITY. 



525 



produced by the resiliency of muscular tissue, in which that curious property, called 

 muscular tonicity, is more or less involved. Movements of this kind are never excited 

 by nervous, galvanic, or other stimulus, but they consist simply in the return of movable 

 parts to a certain position after they have been displaced by muscular action, and the 

 reaction of tubes after forcible distention, as in the walls of the large arteries. 



Elastic Tissue. Most writers of the present day adopt the division of the elements of 

 elastic tissue into three varieties. This division relates to the size of the fibres ; and all 

 varieties are found to possess essentially the same chemical composition and general 

 properties, including the elasticity for which they are so remarkable. On account of the 

 yellow color of this tissue, presenting, as it does, a strong contrast to the white, glisten- 

 ing appearance of the inelastic fibres, it is frequently called the yellow elastic tissue. 



The first variety of elastic tissue is composed of small fibres, generally intermingled 



FIG. 148. Small elastic fibres, from the peritoneum ; 

 magnified 350 diameters. (Kolliker.) 



FIG. 149. Larger elastic fibres. (Eobin.) 



with fibres of the ordinary inelastic tissue. These are sometimes called, by the French, 

 dartoic fibres. They possess all the chemical and physical characters of the larger fibres, 

 but are excessively minute, measuring from 25 ^ 00 to -^-g- or ^Vo of an inch in diameter. 

 If we add acetic acid to a preparation of ordinary connective tissue, the inelastic fibres 

 are rendered semitransparent, but the elastic fibres are unaffected and become very dis- 

 tinct. They are then seen isolated, that is, never arranged in bundles, generally 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 pursue a wavy 

 course between the bundles of inelastic fibres in the areolar tissue and in most of the ordi- 

 nary fibrous membranes, and here they exist as an accessory anatomical element. They 

 are found in greater or less abundance in the situations just mentioned ; also, in the liga- 

 ments (but not the tendons) ; in the layers of involuntary muscular tissue ; the true skin ; 

 the true vocal cords ; 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 the ordinary connective tissue exists. 



The second variety of elastic tissue is composed of fibres, larger than the first, ribbon- 

 shaped, with well-defined outlines, anastomosing, undulating or curved in the form of the 

 letter S, presenting the same curled ends and sharp fracture as the smaller fibres. These 

 measure from -^-^ to ^Vfr of an inch in diameter. Their type is found in the ligamenta 

 subflava and the ligamentum nucha3. They are also found in some of the ligaments of 

 the larynx, the stylo-hyoid ligament, and the suspensory ligament of the penis. The 

 form and arrangement of these fibres may be very strikingly demonstrated by tearing 

 off a portion of the ligamentum nuchse and lacerating it with needles in a drop of acetic 



