HISTOLOGY 



lOI 



the source of gelatin and glue. These collagenous fibers are only slightly 

 elastic. They may be branched. Each fiber is a bundle of very delicate 

 fibrils. Exceedingly flattened cells with flat nuclei appear as if clinging 

 closely to the surface of a fiber. These connective-tissue cells or fibro- 

 cytes are presumably the agencies which have brought about the produc- 

 tion of the fiber in the intercellular matrix. 



Elastic fibers are much finer than collagenous fibers and difi"er from 

 them chemically in being composed of elastin which is not a source of 

 gelatin. An occasional elongated fibrocyte may be seen stretching along 

 the surface of a fiber (Fig. 97). Elastic 

 fibers commonly occur inter-mingled with 

 collagenous fibers. 



Connective tissue forming a loose open 

 mesh-work, as does the subcutaneous tissue 

 lying between the skin and the muscle of 

 the body, is called areolar tissue. 



Tendons and ligaments are connective- 

 tissue structures highly adapted to resisting 

 tensile strain. They consist of coarse 

 collagenous fibers arranged in compact 

 bundles. Tendons are inelastic. 



Chroma tophores, pigment cells (Fig. 

 96S), may occur in connective tissue, 

 especially in the dermal layer of the skin. 

 The specific pigment appears as granules 

 lying in the cytoplasm. Black pigment 

 (melanin) is most common and cells con- 

 taining it are called melanophores. Chro- 

 matophores are usually richly branched. The pigment may at one time 

 be distributed throughout the processes ("expanded" phase), at another 

 time densely massed in the central part of the cell ("contracted" phase). 

 Some pigment cells are migratory. 



Fig. 97. — A, elastic fibers of 

 the subcutaneous areolar tissue of 

 a rabbit. B, cells related to 

 elastic fibers, as seen after treat- 

 ment with acetic acid; from sub- 

 cutaneous tissue of a pig embryo. 

 (From Bremer, Text-book of 

 Histology: A, after Schafer; B, 

 after Mall.) 



Skeletal Tissues 



Notochord. The essential notochord material consists of cells each 

 of which contains a relatively enormous vacuole occupied by a substance 

 of fluid, or possibly gelatinous, consistency. The cytoplasm of the dis- 

 tended cell is so stretched that it appears as the thinnest possible layer 

 surrounding the vacuole. The very flat nucleus occasions a bulge in the 

 contour of one side of the cell (Fig. 98). The outer cell-membrane, 

 while very thin, is probably of semi-rigid consistency. Seen under the 

 microscope, this tissue looks like a mass of soap bubbles crowded closely 



