The hump in the middle of bridges (5)
I believe the answer is:
ridge
'the hump' is the definition.
(thesaurus)
'middle of bridges' is the wordplay.
'middle of' means to look at the middle letters.
The centre of 'bridges' is 'RIDGE'.
'in the' is the link.
(Other definitions for ridge that I've seen before include "Line of raised ground" , "Part of mountain" , "High ground" , "German Baltic port, Buxtehude home" , "Narrow elevated strip" .)