Unlike ruminants , however , which possess the rumen ( a specialized stomach for bacterial fermentation ) , the hoatzin has an unusually large crop , folded in two chambers , and a large , multi-chambered lower oesophagus .
Unlike ruminants , however , which have the rumen ( a specialized stomach for bacterial fermentation ) , the hoatzin has an unusually large crop , folded in two chambers , and a large , multi-chambered lower oesophagus .