Most have no more than 22 teeth and some have ever-growing cheek teeth as well as the incisors. The cheek teeth, the molars and premolars, are the gristmill for whatever food the rodent takes in. They are often massive and the complex structure of convoluted layers of enamel and dentine are often used as taxonomic indicators. The arrangement of the grinding surface and the muscle attachment pattern for the great masseter muscles are the criteria on which suborder classification is based. The masseter muscles will be discussed in greater detail later.
Many rodents have cheek pouches for the storage and carrying of food, nesting material, etc.
The openings to the cheek pouches may be external, as in the gopher, or internal, as in the hamster. These pouches are quite capacious, often reaching past the shoulders when loaded. They are emptied by pushing from behind with the forepaw. Most rodents are relatively small animals as evidenced by the mice, rats and squirrels frequently encountered, although the largest rodent, the capybara, may reach 100 pounds and the North American beaver may grow to 60 pounds. All rodents have a basic compact body with short legs, the exceptions occurring under extenuating conditions.