The enemy evacuating Nashville.
Mobile, Dec. 19.
--A special dispatch to the Advertiser and Register, from Murfreesboro', says that prisoners from Nashville report the enemy gradually evacuating the city, in the direction of Bowling Green.
They are removing their heavy guns across the river.
This movement is supposed to be with the object of reinforcing Grant's army.
Wm. H. Polk died on the 13th Inst.