Anatomical pouch (3)
I believe the answer is:
sac
'anatomical pouch' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sac that I've seen before include "Animal or vegetable pouch" , "Pouchlike structure" , "Bag-like cavity" , "Bodily cavity enclosed by a membrane" , "Bodily pouch" .)