38 Introduction 



Three other kinds of modified areolar connective tissue are found 

 in living materials. These include reticular, elastic, and fibrous. Reticu- 

 lar tissue is formed of a network of white fibers in contact with small 

 flat cells, and with numerous small spaces between the fibers. This 

 tissue forms the framework of much of the lymphatic tissue, and is also 

 found in the mucous membranes of numerous organs. The matrix of 

 elastic connective tissue contains many branching yellow fibers and a 

 few white fibers. This tissue is quite elastic and is found in the res- 

 piratory tract. The matrix of fibrous connective tissue, in contrast to 

 that of the others, contains many long collagenous fibers cemented into 

 bundles. This produces a strong white tissue. It forms the heavy 

 bands for attaching muscles to bones and for binding bones together. 



Other important types of connective tissue are the cartilage (Fig. 

 26) and bone (Fig. 28) that make up the skeletal framework of the 

 body. 



3. Vascular Tissue. Blood and lymph. These tissues serve 

 to distribute oxygen and food and to remove waste materials from the 

 cells of the body. (Fig. 52.) 



4. Muscular Tissues. All these tissues are distinguished by the 

 fact that they are able to contract. They consist of specialized muscle 

 cells attached to bones and in the internal organs. The appearance of 

 this tissue microscopically differs with the type of work performed. 

 (Fig. 34.) 



5. Nervous Tissue. This tissue is specialized for the transmis- 

 sion of sensory impulses. (Fig. 57.) 



6. Reproductive Tissue. This tissue consists of the specialized 

 cells of the ovary and testes which produce the eggs and sperm. (Figs. 

 76 and 78.) 



Glands. — Almost any cell may at times produce secretions; but 

 those cells which specialize in this function are known as glands (Fig. 

 5). A gland may consist of but a single cell or it may consist of many 

 cells. The secretions of these specialized cells may be secreted onto a 

 surface, directly into the blood, or into some body cavity. Some glands 

 store up their products and discharge them at one time, others liberate 

 them continuously. 



At times the terms excretion and secretion are used interchange- 

 ably when speaking of the products produced by glands. This is due 

 in part to the fact that it is often difficult to distinguish between these 



