IV.  In  some  joints,  very  particularly  in  the
knees,  there  are  loose  cartilages  or  gristles  between
the  bones,  and  withiii  the  joint,  so  that  the  ends
of  the  bones,  instead  of  working  upon  one  another,
work  upon  the  intermediate  cartilages.  Chesel-
den  has  observcd,§  that  the  contrivance  of  a  loose
ring  is  practised  by  mechanics,  where  the  friction
of  the  joints  of  any  of  their  macliines  is  great ;  as
between  the  parts  of  crook-hinges  of  large  gates,
or  under  the  head  of  the  male  screw  of  large  vices.
*  Chos.  Anat.  p.  255.  ed.  7.  t  Ih.  p.  35.
i  lb.  p.  30.  §  lb.  p.  13.
