EPITHELIAL TISSUES 9 



lower border of the cells. As they approach the surface 

 the layers become flatter and more scale-like and possess less 

 vitality. As the outer layers are worn away the lower more 

 vigorous layers push upward to the surface to take their place. 

 In the middle strata, where the cells are polyhedral in shape, 

 we find the layer of prickle cells which have minute projecting 



FIG. 4. Vertical section of the stratified epithelium of the rabbit's cornea. 



a, anterior epithelium, showing the different shapes of the cells at various denths 



from the free surface; b, a portion of the substance of cornea. (Kirkes after Klein.) 



spines by which they are connected together. This layer is 

 sometimes called the stratum spinosum. Just below this is the 

 stratum germinativum, or germinating layer. 



(2) Columnar Epithelium. (a) The simple columnar va- 

 riety consists of a single layer of column or rod-shaped cells, set 

 upright, longitudinally striated and containing oval-shaped 

 nuclei. This variety is found in the lining of the stomach and 

 intestines. 



(b) In the stratified columnar variety the single layer of cells 

 is replaced by several layers and the superficial elements alone 

 are typical. This type is found in the vas deferens. Ciliated, 

 it occurs in the Eustachian tube, lachrymal ducts, respiratory 

 part of the nasal fossae, ventricle of larynx, trachea and bronchi, 

 epididymis and first part of vas deferens. 



(3) Modified Epithelium. (a) Ciliated epithelium is more 

 common with the columnar variety than with any other. Each 



