IS 



NORMAL HISTOLOGY. 



ficial layers of stratified squamous epithelium. The position of the nucleus 

 also varies with the situation of the cells, since within those next the base- 

 ment membrane the relatively large nucleus lies near the subjacent con- 

 nective tissue, while within the cells of the middle and superficial strata the 

 nucleus, comparatively small, is placed about the centre of the cell. The 

 irregularly polyhedral cells of the deeper strata frequently are connected by 

 delicate protoplasmic processes which bridge the intervening intercellular 

 clefts (Fig. 17); when such elements are isolated, the delicate connecting 



FIG. 18. Transitional epithelium from the bladder. 

 X3- 



FIG. 19. Simple columnar epithelium from In- 

 testinal mucosa. X 750. 



threads are broken and appear as minute spines besetting the so-called prickle 

 cells. In certain localities, as in the urinary bladder, the columnar cells of 

 the deepest layer rapidly assume the scaly character of the superficial elements. 

 Such epithelium possesses relatively few layers and is often described as 

 transitional epithelium, a modification of the stratified squamous variety. 



Columnar Epithelium. When consisting of a single layer of pris- 

 moidal elements, the epithelium constitutes the simple columnar variety, 

 which is much more widely distributed than the corresponding squamous 

 group, the lining of the stomach and of the intestinal tube being important 

 examples. When the single layer of cells is replaced by several, as in the 

 stratified columnar epithelium, the superficial elements alone are typically 

 columnar. The free ends of the prismoidal cells frequently present cyto- 

 plastic specializations in the form of a cuticidar border or of cilia, while their 

 ends which rest upon the basement membrane are pointed, club-shaped, or 

 forked. The intervals formed by such irregular contours are occupied by 

 the smaller cells of the deeper stratum. Each cell is provided with a 



FIG. 20. Stratified columnar epithelium from 

 vas deferens. X 500. 



FIG. 21. Goblet-cells from epithelium lining 

 large intestine. X 500. 



nucleus, which is situated about the middle within the superficial elements 

 and nearer the base within the deeper ones. The surface cells often contain 

 collections of mucous secretion and, in consequence, become distended into 

 conspicuous chalice forms known as goblet-cells. Such modified elements 

 occur in great profusion within the epithelial lining of the large intestine 

 and of the respiratory tract. 



Modified Epithelium. In order to meet particular work, beyond 

 the mere function of protection, epithelial cells may undergo profound mod- 

 ification or high specialization. Thus, in order to produce a current favor- 



