32 EPITHELIUM [CH. III. 



application of caustic potash, which rapidly causes them to swell 

 and assume their original form. Their nuclei, however, have 

 disappeared. 



The squamous cells exist in the greatest number of layers in the 

 epidermis or superficial part of the skin; the most superficial of 



FIG. 47. Vertical section of the stratified epithelium of the rabbit's cornea, a, anterior epithelium, 

 showing the different shapes of the cells at various depths from the free surface ; b, a portion of the 

 substance of cornea. (Klein.) 



these are being continually removed by friction, and new cells from 



below supply the place of those cast off. 



In many of the deeper layers in the mouth and skin the outline 



of the cells is very irregular, in consequence of processes passing 



from cell to cell across these intervals. 



Such cells (fig. 48) are termed " ridge and furrow," " cogged " or 



"prickle" cells. These "prickles" are prolongations of the intra- 



cellular network which run across from cell to cell, thus joining them 



together, the interstices being filled by 

 lymph and transparent inter-cellular 

 cement substance. When this increases 

 in quantity in inflammation the cells 

 are pushed further apart, and the con- 

 necting fibrils or " prickles " are elon- 

 gated and therefore more clearly visible. 



This connection of cell to cell is sometimes 

 spoken of as continuity of protoplasm ; the same 

 occurs in involuntary muscular tissue. It is 

 very marked in the tissues of many plants. 



The columnar cells of the deepest 

 layer are distinctly nucleated; they 

 multiply rapidly by division ; and as new cells are formed beneath, 

 they press the older cells forwards to be in turn pressed forwards 

 themselves towards the surface, gradually becoming flatter in shape 

 and horny in composition until they are cast off from the surface. 



Stratified epithelium is found in the following situations: (1) 

 Forming the epidermis, covering the whole of the external surface of 

 the body; (2) Covering the mucous membrane of the nasal orifice, 



FIG. 48. Jagged cells from the middle 

 layers of stratified epithelium, from a 

 vertical section of the gum of a new- 

 born infant. (Klein.) 



