Chap. 7 



TISSUES 



109 



Fig. 7.2. Cuboidal or low simple columnar epithelium: A, lining of a collecting 

 tubule in the kidney of a monkey; B, in the thyroid gland of a monkey. These 

 cells produce the thyroid secretion. xl200. (Courtesy. Nonidez and Windle: 

 Textbook of Histology, ed. 2. New York, McGraw-Hill Book Co., Inc., 1953.) 



due to the epithelium on their bodies and in their kidneys that the animals of 

 ancient time could leave the sea and gradually become adjusted to living in 

 fresh water or on land. The epidermis or outer layers of human skin which is 

 formed of epithelial cells is in general about as thick as tissue paper. Yet a bit 

 of vinegar dropped on broken and unbroken skin are vividly different expe- 

 riences. In certain regions, the epidermis is many-layered, as on the palms of 



m. 



lil 



Sgi^^ligg:^^^ 



Fig. 7.3. Columnar epithelium with motile cilia (c) lining the trachea of a 

 monkey. Mucous or goblet cells (g) secrete the mucus (m) that passes through 

 the membrane at one end of the cell and spreads over the inner surface of the 

 trachea. The delicate non-cellular basement membrane (b) separates the epi- 

 thelium from the loose connective tissue beneath. A lymphocyte ( 1 ) is migrating 

 through the epithelium. X1200. (Courtesy, Nonidez and Windle: Textbook of 

 Histology, ed. 2. New York, McGraw-HillBook Co., Inc., 1953.) 



