Bionis' Interior (Carcass) (巨神胎内／骸, Inside the Giant / Carcass) is a Field Track in Xenoblade Chronicles, composed and arranged by Manami Kiyota. It is track 20 of disc 4 from the Xenoblade Original Soundtrack. This music is heard when the party enters the Bionis' Interior for the first time, connecting from Satorl Marsh to Makna Forest. This theme will play in that area up until the events at the Mechonis Core.
Motifs from this song are used for "Urayan Tunnels" in Xenoblade Chronicles 3.