Possible Clues:

• Anatomical sac
• Sac that facilitates motion
• Fluid-filled sac
• Anatomical pouch
• Sac between a bone and tendon
• Bulge under radius, say, aching initially
• Part of joint treasurer's brief
• Pouch containing last fragments of china vessels Wheeler initially unearthed, brought up to capital of Brunei
• Pouch aboard airline guards regularly ignored
• Sac near human joints