CELL ULTUASTKL'CTURE IN MAMMALS 



'aSESii.. 



Fig. 13. Detail of a basal cell of the human epi- 

 dermis. The cytoplasm is run through by abundant 

 tonofilaments (Tf) most of which are sectioned 

 longitudinally. They display a hollow structure 

 (arrows) and originate from dense areas (X) of the 

 plasma membrane which faces the basement mem- 

 brane (BM). Magnification 83, 000 X 



each other m the formation of the tonofibrils. 

 The tonofibrils originate from and terminate 

 at the desmosomes which are buttonhke 

 structures associated with the plasma mem- 



Cl 



^H^mSi^ 



^i^-*' 



a2ju 



Fig. 14. Cell l)()iiiul:uu'.-> ui luu adjacent cells 

 (Cl and C2) of the basal part of the human epider- 

 mis. The cells are highly interdigitated and the 

 mutual attachment established through desmo- 

 somes (De) in association with which the in- 

 tercellular space is wider than elsewhere. The 

 tonofilaments (Tf) terminate (or originate) at the 

 desmosomes. Magnification 90,000X 



brane (Fig. 14). Histochemical and bio- 

 chemical tests prove that the main com- 

 ponent of the tonofilaments is keratin, a 

 tough noncontractile, in young tissue quite 



107 



