CHAPTER II. 

 THE ELEMENTARY TISSUES. 



THE tissues which make up the various organs and parts 

 of the body may be divided into the following groups: (i) 

 Epithelial tissue, (2) connective tissue, (3) muscular tissue 

 and (4) nervous tissue. 



The Epithelial Tissues. 



The epithelial tissues include those which form the cover- 

 ing for the body, the lining of the digestive canal, the respira- 

 tory tract and the genito-urinary tract. They also constitute 

 the derivatives of the epidermis, such as nails, hair, seba- 

 ceous glands, and the lining of the glands connected with the 

 digestive and genito-urinary systems. 



These tissues are composed of cellular and intercellular 

 elements and perform various functions in different parts of 

 the body. In the skin where they constitute the epidermis, 

 they protect the delicate surface of the true skin beneath ; in 

 the alimentary and genito-urinary canals they aid in secre- 

 tion and excretion ; in the respiratory system they preserve 

 an equable temperature, while in all internal parts they yield 

 lubricants. 



These tissues are characterized by the preponderance of 

 the cellular over the intercellular elements. The intercellular 

 structure consists of a cement substance which holds the cells 

 together and through which the food for the cells is ab- 

 sorbed. They contain no blood-vessels and no nerves. The 

 tissue usually rests upon a basement membrane, or membrana 

 propria, which is a modification of the connective tissue be- 

 neath. 



