The  OLFACTORY  CELLS  occupy  a  unique  position  among  neuro-epithe-
lial  cells  in  that  they  are  true  nerve  or  ganglion  cells.  They  possess  a
small  cytoplasmic  body  and  two  processes,  a  distal  and  a  central.  Their
nuclei  are  spherical  and  are  disposed  in  several  rows  beneath  the  nuclear
zone  of  the  sustentacular  cells ;  thus  they  form  a  broad  zone  of  spherical
nuclei.  The  distal  process  of  the  olfactory  cell  projects  as  a  slender
filament  whose  free  end,  carrying  several  fine  cilia,  reaches  the  surface  of


298


THE  EESPIEATOEY  SYSTEM


the  membrane  through  a  pore-like  opening  in  the  cuticular  membrane
which  is  formed  by  the  cuticle  of  adjacent  sustentaciilar  cells.  The
central  process  of  the  olfactory  cell  penetrates  to  the  tunica  propria  and
becomes  a  non-medullated  nerve  fiber  of  one  of  the  many  rami  of  the
olfactory  nerve ;  it  passes  to  the  olfactory  bulb,  where  its  terminal  arbori-
zation with  the  dendrites  of  the  mitral  cells  forms  the  olfactory  glom-
eruli.
The  BASAL  CELLS  are  flattened  cells  which  form  the  deepest  nuclear
zone  of  the  olfactory  neuro-epithelial  layers.     Their  cytoplasm  is  finely

granular  and  their  nu-
clei are  ovoid  or  flat-
tened. Frequently  they
send  a  short  process  be-
tween the  branched  ends
of  the  sustentacular  cells.
Many  small  nerve
trunks  occur  in  the
tunica  propria.  The
great  majority  of  these
are  non-medullated  and
are  formed  by  the  cen-
tral processes  of  the  ol-
factory cells,  which  proc-
esses are  true  axons.
