Plate 12 



A. Portion of a typical epidermal cell forming a hard keratin, in this case 

 from the feather follicle, showing the edge of a nucleus (l.h.s.), the 

 double nuclear membrane, NM, mitochondria, m, and/, fibrils of fibrous 

 keratin. The nucleus contains short lengths of filaments and the cyto- 

 plasm contains large numbers of dense particles P, not associated with 

 membranes. 



B. Fibrils, F, of fibrous keratin in the bulb region of the human-hair 

 follicle. Each fibril is seen to be composed of fine filaments,/. Note the 

 dense particles, P, which crowd the cytoplasm. 



C. A number of desmosomes distributed along a very convoluted contact 

 between two cells in the germinal layer of rat skin where the desmosomes 

 are not yet associated with cytoplasmic filaments. Each desmosome con- 

 sists of a paired thickening of the plasma membranes backed in each cell 

 by a dense amorphous deposit. 



