1. Wash the gourd, cut in half length wise, remove and discard the seeds, and cut the flesh into 1" x 2" pieces.
2. Boil the bones in the water, skimming off the scum as it forms. After a while, add the bitter gourd and fish sauce, and put the lid on the pot. Do not stir. Continue cooking until the gourd is well done, and then turn off the heat.
3. Sprinkle with the coriander greens and serve hot.