The underground structure of the Musa consists of
corm = similar to a bulb in function, but more of a fleshy mass in structure.
rhizome = tuberous runners that link corms together.
roots = extended from corms, and occasionally from rhizomes.
A lateral root from a corm may develop into a rhizome provided it is developing from a corm. An adventurous rhizome can develop corms at nodes or the terminal end provided it is developing from a corm. Pups sprout from corms -- either on the side of the "mother" corm or from a newly developed one on a lateral rhizome.
Here's a helpful diagram from Gabe:
