… parts of which being low, best left incomplete (5)
I believe the answer is:
lobes
'parts of which' is the definition.
'lobes' can be an answer for 'parts' (lobe is a kind of part). I am not sure about the rest of the definition.
'low best left incomplete' is the wordplay.
'low' becomes 'lo' (I can't explain this - if you can you should believe this answer much more).
'left incomplete' means to remove the last letter.
'best' with its final letter taken away is 'bes'.
'lo'+'bes'='LOBES'
'being' acts as a link.
(Another definition for lobes that I've seen is " Fleshy parts of ears".)