{HEAD ~ Each stem} is movable between a withdrawn position and {TAIL ~ an extended position} with respect to the base, such that the second end projects from the base when the stem is in the extended position 
is movable between
{ HEAD ~ Each stem } is movable between a withdrawn position and { TAIL ~ an extended position } with respect to the base , such that the second end projects from the base when the stem is in the extended position
HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH