ELASTIC TISSUE. 67 



property in a very high degree, and is employed wherever an extensible 

 and highly elastic material is required in the animal structure. 



Examples of this texture on a large scale are seen in the horse, ox, 

 elephant, and other large quadrupeds, in which it forms the great 

 elastic ligament, called lifiamentum nuclim, that extends from the spines 

 of the vertebrae to the occi[)ut, and aids in sustaining the head ; in the 

 same animals it also forms an elastic subcutaneous fascia, which is 

 spread over the muscles of the abdomen and assists in supporting the 

 contents of that cavity. In the human body it is met with chiefly in 

 the following situations, viz, :-— 



1. Forming- the Ugamcnta suhffava, which extend between the arches of 

 adjacent vertebrae ; these ligaments, while they permit the bones to be drawn 

 apart in flexion of the body, aid in restoring and maintaining- their habitual ap- 

 IDroximation in the erect posture — so far. therefore, relieving the constant effort 

 of the erector muscles. There is. moreover, an obvious advantage in having an 

 elastic band in this situation, instead of an ordinary ligament. ■s\-hich would be 

 thrown into folds when the liones are approximated. 2. Constituting the chief 

 part of the stylohyoid, thjTohyoid. and cricothjToid ligaments, and those named 

 the vocal cords. Also extending, in fonn of longitudinal bands, underneath the 

 mucous membrane of the windpipe and its ramifications. 8. Entering, along 

 Tvith other textures, into the formation of the coats of the blood-vessels, esjie- 

 cially the arteries, and conferring clasticitj' on these tubes. 4. Beneath the 

 mucous membrane of the gullet and lower jiart of the rectiim, also in the tissue 

 which surrounds the muscular coat of the gullet externally. 5. In the tissue 

 which lies under the serous membranes in certain jaarts. G. In manj^ of the 

 fasciii3. where it is mixed with much areolar tissue. 7. Largely in the suspensory- 

 ligament and subcutaneous tissue of the penis. 8. In considerable quantity in 

 the tissue of the skin. 9. In the enclosing capsule and trabecular tissue of the 

 spleen. 



The elastic tissue in its purest and most typical condition, such as is 

 seen in the ligamentum nuchaj of quadrupeds and the ligamenta sub- 

 flava of the human spine, has a yellow colour more or less decided ; it 

 is extensible and elastic in the highest degree, but is not so strong as 

 ordinary fibrous ligament, and it breaks across the direction of its 

 fibres when forcibly stretched. Its fibres may be easily torn separate 

 in a longitudinal direction ; they are often gathered into irregular 

 fasciculi which run side by side, but join at short distances by slips 

 with one another, and are further connected by areolar tissue, which is 

 always intermixed with them in greater or less quantity. Elastic liga- 

 ments are also covered outwardly with a sheath of areolar tissue. 



When the elastic fibres are mixed up with a large proportion of some 

 other kind of tissue, their yellow colour may not appear, but they can 

 always be recognised by their microscopic characters. "When viewed 

 under a tolerably high magnifying power, they appear quite trans- 

 parent, with a remarkably well-defined dark outline (fig. 40). They 

 run side by side, following a somewhat bending course, but with bold 

 and wide curves, unlike the undulations of the white connective fila- 

 ments. As they proceed they divide into branches, and join or 

 anastomose together in a reticular manner. Elastic networks may be 

 composed of fine fibres with Avide meshes ; in other parts the elastic 

 fibres are larger and broader and the intervening spaces narrower, so 

 that the tissue may even acquire a lamellar character and present 

 the^ appearance of a homogeneous membrane, which may be either 

 entire, or with gaps or perforations at short intervals, in which case 



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