pocket mouse, small jumping rodent of W North America and as far south as N South America. More closely related to the squirrel than the true mouse, the pocket mouse gets its name from the fur-lined cheek pouches in which it carries its food. It varies in length from 3 to 12 in. (7.6–30.5 cm) according to the species and has hind legs elongated for jumping. Species of the genus Perognathus are soft furred; species of the genera Liomys and Heteromys have stiff, flattened spines mixed in with the fur. The pocket mouse is a solitary, nocturnal animal, living in grass-lined burrows in desert and semidesert regions; one Heteromys species lives in humid forests. The rodent feeds on seeds and other vegetable matter. It can live for long periods without free water by utilizing the moisture available from food and its own digestive processes and by secreting concentrated urine. Females give birth to several litters a year, each litter containing from one to eight young. Gestation takes from 24 to 33 days. Pocket mice have many natural enemies but in captivity have lived as long as five years. They are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Rodentia, family Heteromyidae.