720 



STRUCTURE OF EPIDERMIS AND EPITHELIUM. 



Fig. 380. 



surface of the True Skin, after the more consistent layers of the 

 Cuticle have been raised by a blister. The alteration which the 



cells of the external layers have 

 undergone, tends to obscure their 

 character ; but if any fragment of 

 Epidermis be macerated for a little 

 time in a weak solution of Soda 

 or Potass, its dry scales become 

 softened, and are filled-out by im- 

 bibition into rounded or polygonal 

 cells. The same mode of treatment 

 enables us to make out the cellular 

 structure in Warts and Corns, which 

 are Epidermic growths from the 

 surface of papilla? enlarged by hy- 

 pertrophy. 

 ^Vi^lr* J^^ 563. The Epithelium may be de- 



signated as a delicate Cuticle, 

 covering all the free internal sur- 

 faces of the body, and thus lining 

 all its cavities, canals, &c. Save in 

 the mouth and other parts in which 

 it approximates to the ordinary 

 Cuticle both in locality and in 

 nature, its Cells (Fig. 381) usually 

 form but a single layer; and are so 

 deficient in tenacity of mutual ad- 

 hesion, that they cannot be detached 

 in the form of a continuous Mem- 

 brane. Their shape varies greatly ; 

 for sometimes they are broad, flat, 

 and scale-like, and their edges approximate closely to each other, 

 so as to form what is termed a ' pavement ' or ' tesselated ' Epi- 

 thelium ; such cells are observable 



Pigment-cells from tail of 

 Tadpole : — a, a, simple forms 

 of recent origin ; 6, b, more 

 complex forms subsequently 

 assumed. 



Fig. 381. 



Detached Epithelium- cells a, 

 with nuclei b, and nucleoli c, from 

 Mucous Membrane of mouth. 



on the web of a Frog's foot, or on 

 the tail of a Tadpole ; for, though 

 covering an external surface, the 

 soft moist Cuticle of these parts 

 has all the characters of an Epi- 

 thelium. In other cases, the 

 cells have more of the form of 

 cylinders, standing erect side-by- 

 side, one extremity of each cy- 

 linder forming part of the free 

 surface, whilst the other rests 

 upon the membrane to which 

 it serves as a covering. If the 

 cylinders be closely pressed-toge- 



