Reins
(i.e. kidneys). In the ancient system of physiology the kidneys were believed to be the seat of desire and longing, which accounts for their often being coupled with the heart. Ps 7:9; 26:2; Jer 11:20; 17:10, etc.
Bibliography Information Smith, William, Dr "Definition for 'Reins' Smiths Bible Dictionary". bible-history.com - Smiths; 1901.