Cheek pouches
A hamster's cheek pouches are paired pockets of oral lining that extend backward along the sides of the neck as far as the shoulder blades. Their walls are thin, muscular and elastic, contain no salivary glands and stay dry inside, so seeds carried in them are stored, not digested. The pouches are filled through the mouth, emptied by pressing the forepaws along the cheeks, and each is anchored by a retractor muscle running back toward the shoulder; the whole pouch can be everted, turned inside out like a pocket.
A two-chambered stomach
Unlike the simple stomach of a rat or mouse, the hamster stomach has two compartments separated by a narrow, muscular waist. The first is the nonglandular forestomach, lined with keratinized squamous epithelium and holding a microbial population that begins fermenting food at a nearly neutral pH — a small-scale echo of what happens in a ruminant's forestomach. The second, glandular compartment secretes the acid and enzymes of ordinary gastric digestion.
Intestine, cecum, and coprophagy
Beyond the stomach, the small intestine carries out enzymatic digestion and absorbs most nutrients, and a large sacculated cecum ferments fiber into short-chain fatty acids the animal can use. Like rabbits and guinea pigs, hamsters routinely re-ingest feces, recovering microbial protein and B vitamins produced in a chamber downstream of the main absorptive gut. As in other rodents, movement through the tract is one-way: hamsters cannot vomit.