Primate kept in by section of low wall (7)
I believe the answer is:
parapet
'low wall' is the definition.
(I've seen this before)
'primate kept in by section' is the wordplay.
'primate' becomes 'ape' (large primate).
'kept in by' means one lot of letters goes inside another.
'section' becomes 'part' (synonyms).
'ape' going inside 'part' is 'PARAPET'.
'of' is the link.
(Other definitions for parapet that I've seen before include "Wall's top" , "place of safety?" , "Low protective wall along edge of roof or bridge" , "Roof-edge wall" , "Militarily, it protects" .)