EPITIIMLIUiM 75 



capsule of the renal corpuscle, in the descending arm of Henle's loop 

 of the uriniferous tubule, in the retina in the form of pigmented cells, 

 and on the posterior surface of the anterior lens capsule. 



(b) Simple columnar epithelium consists of a single layer of elon- 

 gated cells. The bases of the cells are usually separated from the 

 underlying connective tissue by a basement membrane. The 

 nucleus is, as a rule, in the deeper part of the. cell, near the basement 

 membrane. Many of these cells have prominent thickened free 

 borders or cuticulse. This form of cpithehum is often ciliated. 

 The height of the cell varies greatly, there being all gradations 

 from Jiigh cohmmar to low cuhoidal. Simple columnar epithelium 

 lines the gastro-intestinal canal, the uriniferous tubule (excepting 

 the descending arm of Henle's loop), simple tubular glands, the 

 ducts of some compound tubular glands, the smaller bronchi, 

 the membranous and penile portions of the male urethra, and the 

 gall-bladder. 



In simple columnar epithelium, in addition to the single row of 

 epithehal cells, there are found lying near the basement membrane, 

 between the bases of the epithelial 

 cells, small, spherical, or irregular 

 cells, which frequently show mitosis 

 and which are known as replacing 

 cells. They appear to develop 



into columnar epithehal cells as Fig. iS. -Diagram of Pseudostratified 



they are needed to replace older Epithelium, showing Nuclei situated at 



cells. The so-called pseudostrati- 

 fied epithelium is a form of simple columnar epithelium, in which, 

 from crowding of the cells, the nuclei have come to lie at different 

 levels, thus giving the appearance of stratification (Fig. i8). 



Stratified Epithelium 



In stratified epithelium the cells are arranged in more than one 

 layer. 



(a) Stratified squamous epithelium is developed from simple 

 epithelium by the growth of new cells between the old cells and the 

 underlying connective tissue. It consists of several layers of cells. 

 The number of layers varies but the shape and arrangement of the 

 cells are quite characteristic. The cells of the deepest layer, those 

 lying on the basement membrane which separates the epithelium 



