Link and Princess Ruto are now seperated thanks to Bigocto. Link will have to explore the rest of Jabu-Jabu's belly on his own, because he won't find the princess until he faces Barinade.
Bridge the Gap
Ride the platform up from the Bigocto room, and you'll encounter two wriggling appendages protruding from Jabu-Jabu's flesh. Strike these unusual organs with the boomerang to stabilize them.
The Final Room
At last, Link can use the two small boxes which he found near the entrance so long ago. Dropping a box on the switch will allow you to enter a huge cavernous room filled with Biri.