It looks like belly rot. I picked this up from another website:
Scale Rot (Neocrotic Dermatitis) appears as enlarged, discolored (rust or reddish-brown), fluid filled scales.
Possible ulceration and breakdown of the skin and underlying tissue. Generally appears on the ventral scales (belly), and can be in one long continuous area or in separate spots. This is a bacterial infection that can be caused by damp substrate, inadequate temperatures, and dirty enclosures. Bad cases will also have blisters, and will require draining by your vet. Serious cases are life-threatening.
Immediately clean the enclosure thoroughly. Raise ambient temperature to 88-90 degrees.
You must keep your snake warm and dry during the recovery process. If your snake tends to soak in the water bowl, it may be necessary to remove the larger bowl and replace it with a very small dish that would
not allow soaking but still provide drinking water.
Clean the entire affected area by swabbing with a 50/50 hydrogen peroxide/water solution.
Must be thorough to treat the entire area because the damaged tissue could be in multiple places.
Apply Polysporin or Neosporin to the affected areas twice a day and work it in and under the scales.
Consult your veterinarian as soon as possible, antibiotic injections may be required.
I would recommend Polysporin, as it doesn't have the agent to deaden wounds. Also, this is ony in the circumstance that you do not have a vet around. Even this treatment may not save the poor little thing with that much damage... try to get him to a vet if at all possible. Good luck!
