GELATINOUS TISSUE 



35 



flava of man; the arteries, constituting the fenestrated coat of Henle; the 

 veins iri the lungs and trachea; the stylo-hyoid, thyro-hyoid, and crico- 

 thyroid ligaments; in the true vocal cords; and in areolar tissue. 



Structure. Elastic tissue occurs in various forms, from a structureless, 

 elastic membrane to a tissue whose chief constituents are bundles of fibers 

 crossing each other at different angles; when seen in bundles elastic fibers are 

 yellowish in color, but individual fibers are not 

 so distinctly colored. The varieties of the tissue 

 may be classified as follows: 



a. Fine elastic fibrils, which branch and anas- 

 tomose to form a network. This variety of elastic 

 tissue occurs chiefly in the skin and mucous 

 membranes, in subcutaneous and submucous 

 tissue, in the lungs and true vocal cords. 



b. Thick fibers, sometimes cylindrical, some- 

 times flattened, which branch, anastomose and 

 form a network: these are seen most typically in 

 the ligamenta subflava and also in the ligamentum 

 nuchae of such animals as the ox and horse, in 

 which that ligament is largely developed, figure 40. 



A certain number of connective-tissue cells 

 found in the ground substance between 



are 



FIG. 40. Elastic Fibers 

 from the Ligamenta Sub- 

 flava. X 200. (Sharpey.) 



the elastic fibers which make up this variety of 

 connective tissue, page 34. 



Areolar Tissue. This variety of fibrous tissue has a very wide dis- 

 tribution and constitutes the subcutaneous, subserous, and submucous tis- 

 sue. It is found in the mucous membranes, in the true skin, and in the outer 

 sheaths of the blood vessels. It forms sheaths for muscles, nerves, glands, 

 and the internal organs, and, penetrating into their interior, supports and con- 

 nects the finest parts. 



Structure. To the naked eye it appears, when stretched out, as a fleecy, 

 white, and soft meshwork of fine fibrils, with here and there wider films join- 

 ing in it, the whole tissue being evidently elastic. The openness of the mesh- 

 work varies with the locality from which the specimen is taken. Under the 

 microscope it is found to be made up of fine white fibers, which interlace in a 

 most irregular manner, together with a variable number of elastic fibers. 

 On the addition of acetic acid, the white fibers swell up, and become gelatin- 

 ous in appearance; but as the elastic fibers resist the action of the acid, they 

 may still be seen arranged in various directions, sometimes appearing to pass 

 in a more or less circular or spiral manner round a small gelatinous mass of 

 changed white fiber. The cells of areolar tissues are connective-tissue 

 corpuscles. 



Gelatinous Tissue. Gelatinous connective tissue forms the chief' 



