PIISTOLOGY 143 



chyme cells (Fig. 79 B). In general, they function in supporting 

 the body and connecting or binding together its parts. Sustenta- 

 tive tissues are characterized by a large amount of intercellular 

 material, which is produced by the cells. In the vertebrates, it is, 

 for the most part, this intercellular material that furnishes the sup- 

 porting and connecting qualities. Sustentative tissue may be 

 divided into five sub-classes: connective, cartilage, bone, adipose, 

 and vascular. 



Connective tissues are of three kinds : mucous, in which the inter- 

 cellular material is gelatinous, and which is found in the umbilical 

 cords of mammals (Fig. 79 A) ; reticular, in which there is a mesh- 

 work of connective tissue cells with the interspaces filled with other 

 types of cells, and which forms the groundwork of organs like the 

 spleen (Fig. 79 C) ; and fibrous, in which the intercellular material is 

 composed of fibers, and which is widely distributed as a binding 

 tissue in many organs. The intercellular fibers of fibrous connective 

 tissue are of two kinds, white and elastic. White fibers are very fine 

 and occur in bundles, while elastic fibers are thicker and occur singly. 

 Fibrous connective tissue in which both white and elastic fibers 

 occur is found in the submucous layer of the digestive tract and in 

 the dermis of the skin (Fig. 79 D). Fibrous connective tissue in 

 which white fibers predominate is found in tendons, and that con- 

 taining chiefly elastic fibers is found in the walls of larger arteries 

 and in certain ligaments (Fig. 79 E). The cells of fibrous comiec- 

 tive tissue are spindle-shapetl or irregular in outline and possess 

 relatively little cytoplasm. 



The second sub-class of sustentative tissues is cartilage, which 

 is a supporting tissue. The intercellular material in cartilage is 

 usually hardened by impregnation with mineral salts, chiefly those 

 of calcium. Here the cells are more or less rounded and lie in 

 spaces known as lacunce. Where the matrix between the cells is 

 translucent and apparently structureless, the tissue is called hyaline 

 cartilage, or gristle (Fig. 79 G). Such tissue is found at the ends of 

 long bones, at the ends of ribs, and in the cartilages of the nose and 

 trachea. The cartilage of the external ear contains elastic fibers 

 in its matrix and is, therefore, known as elastic cartilage (Fig. 

 79 H), while that found between the vertebrae has white fibers in 

 its matrix and is fibrous cartilage (Fig. 79 I). 



Bone, or osseous tissue, is characterized by its very hard matrix, 

 which is impregnated with lime salts. There is twice as much inor- 



