7.  The  Distal  Convoluted  Portion  (Intercalary  or  Intermediate
Portion). — This  portion  of  the  uriniferous  jubule  begins  close  to  the
vascular  pole  of  the  renal  corpuscle,  and,  after  several  irregular  contor-


THE  KIDNEY


437


tions  which  are  confined  to  the  region  of  the  cortical  labyrinth,  enters
an  arched  collecting  tubule.  The  distal  is  much  shorter  than  the  proxi-
mal convoluted  portion.  Its  caliber  is  subject  to  great  irregularities,  so
much  so  that  its  early  turns  have  been  characterized  as  the  irregular  or
zigzag  portion  of  the  uriniferous  tubule.  The  epithelium  of  this  section
resembles  that  of  the  proximal  convoluted  portion  but  is  lower,  more
cubc4d£l,^id-sjjiatioG8--are  indistinct.
This  portion  terminates  the  typically  secretory  portion  of  ,the  urinif-
erous tubule.  Beyond  here  the  tubule  possesses  more  the  function  of  a
duct,  hence  its  epithelium  shows  a  decided  change  in  character.  Hith-
erto it  has  possessed  the  peculiar  character,  the  typically  granular  cyto-
plasm, of  a  secreting  type  of  cell.  Beyond  this  section  the  epithelium  is
no  longer  so  granular  but  possesses  a  characteristically  clear  appearance.
The  secretory  and  excretory  portions  of  the  renal  tubule  have  a  separate
embryonic  origin,  and  only  secondarily  unite  to  form  a  continuous  duct.
8.  The  Arched  Collecting  Tubule  (Junctional  Tubule).— This  is
a  short  portion  of  the  uriniferous  tubule  which  connects  the  distal  con-
voluted portion  in  the  cortical"labyrinlh"  with  the  straight  collecting  tu-
bules of  the_cortical  rays.  Its  course  is  characteristically  arched.
