3 o HUMAN PHYSIOLOGY 



When a padding is required, as under the skin and under 

 mucous membranes, the fibres are arranged in a loose felt 

 work to constitute Areolar Tissue. 



In fascia, in tendon sheaths, and in flat tendons, the fibres 

 are closely packed together to form more or less definite 

 layers. In tendons and ligaments the fibres run parallel 

 and close together. In ordinary tendons, where no elasticity 

 is required, the fibres are of the white or non-elastic variety. 

 In ligaments, where elasticity is desirable, the elastic fibres 

 preponderate. 



Lymph Tissue. One peculiar modification of fibrous tissue 

 is often described as a special tissue under the name of Lymph 

 Tissue. It is composed of a delicate network of white fibres, 

 the interstices of which communicate with lymphatic vessels, 

 and contain masses of simple protoplasmic cells, leucocytes, 

 often in a state of active division. So numerous are these 

 that it is impossible to make out the network under the 

 microscope, until they have been removed by washing. 



Lymph tissue is very widely distributed throughout the 

 body, and is of great importance in connection with nutrition. 



II. The spaces of fibrous tissue vary with the arrangement 

 of the fibres. In the loose areolar tissue under the skin 

 they are very large and irregular, in fascia they are flattened, 

 while in tendon, where the fibres are in parallel bundles, they 

 are long channels. 



III. The cells of fibrous tissue (Fibroblasts) vary greatly 

 in shape. In the young tissue they are elongated spindles, 

 from the ends of which the fibres extend. In some of the 

 loose fibrous tissues they retain this shape, but in the denser 

 tissues they get squeezed upon, and are apt to be flattened 

 and to develop processes thrust out into the spaces. 



In certain situations, peculiar modifications of Connective 

 Tissue cells are to be found 



(A) Endothelium. When cells line the larger connective 

 tissue spaces they become flattened, and form a covering 

 membrane, called an endothelium. Such a layer lines all 

 the serous cavities of the body, and the lymphatics, blood 

 vessels, and heart, which are all primarily large connective 

 tissue spaces. To demonstrate the outlines of these cells it 

 is necessary to stain with nitrate of silver, which has a special 



