Follow the extremity (4)
I believe the answer is:
tail
I believe this clue is a double definition.
'follow' is the first definition.
(thesaurus)
'the extremity' is the second definition.
(thesaurus)
(Other definitions for tail that I've seen before include "Dog - or part of one" , "Rear appendage of animal" , "Shadow" , "Flexible part that extends from an animal's rear" , "Dog - end" .)