HISTOLOGY OF EPITHELIAL AND CONNECTIVE TISSUES. 39 



either utilized for tissue construction or for oxidation purposes. In 

 the situations in which adipose tissue is found it seems, by its chemic 

 and physical properties, to assist in the prevention of a too rapid 

 radiation of heat from the body, to give form and roundness, and to 

 diminish angularities, etc. 



Retifoim and adenoid tissue are also modifications of areolar 

 tissue. The meshes of the former contain but little ground sub- 

 stance, its place being taken by fluids ; the meshes of the latter con- 

 tain large numbers of lymph corpuscles. 



Fibrous Tissue. This variety of connective tissue is widely dis- 

 tributed throughout the body. It constitutes almost entirely the liga- 

 ments around the joints, the tendons of the muscles, the membranes 

 covering organs such as the heart, liver, nervous system, bones, etc. 

 All fibrous tissue, wherever found, can be resolved into elementary 

 bundles, which on microscopic examination are seen to consist of 

 delicate, wavy, transparent, homogeneous fibers, which pursue an 

 independent course, neither branching nor uniting with adjoining 

 fibers. A small amount of ground substance serves to hold them 

 together. Fibrous tissue is tough and inextensible, and in conse- 

 quence is admirably adapted to fulfil various mechanical functions 

 in the body. It is, however, quite pliant, bending easily in all di- 

 rections. When boiled, fibrous tissue yields gelatin, a derivative of 

 collagen. 



Elastic Tissue. The fibers of elastic tissue are usually associated 

 in varying proportions with the white fibrous tissue ; but in some 

 structures as the ligamentum nuchae, the ligamenta subflava, the 

 middle coat of the larger blood-vessels the elastic fibers are almost 

 the only elements present, and give to these structures a distinctly 

 yellow appearance. The fibers throughout their course give off many 

 branches, which unite with adjoining branches to form a more or 

 less close network. As the name implies, these fibers are highly 

 elastic, and are capable of being extended as much as sixty per cent, 

 before breaking. 



Cartilaginous Tissue. This form of connective tissue differs from 

 the preceding varieties chiefly in its density. As a rule, it is firm 

 in consistency, -though somewhat elastic. It is opaque, bluish-white 

 in color, though in thin sections translucent. All cartilaginous tissues 

 consist of connective-tissue cells embedded in a solid ground substance. 



