Facts for Kids

Mouth is the name for the opening many animals use to eat, drink, smell, and make sounds. In humans and other land animals this space inside the mouth is called the oral cavity, and it is the very first part of the tube that food travels through on its way to the stomach.

The mouth helps animals take in food, begin chewing or breaking it up, and mix it with saliva. In animals with faces, the mouth is often surrounded by lips and cheeks and holds a tongue and usually teeth, though some animals like birds and many amphibians do not have true teeth.

When animals start life as tiny embryos, the gut— the tube that will carry food— begins to form. Most animals called bilaterians grow a gut with two openings: a mouth at one end and an anus at the other. Scientists name groups by which opening forms first. In some animals the little first opening, called the blastopore, becomes the mouth; in others it becomes the anus and the mouth forms later.

A long time ago, the very first animals probably ate tiny bits of food by engulfing them into body cells. This kind of cell-eating still happens in simple animals like sponges that do not have a real mouth or gut.

Animals with backbones, or vertebrates, have a mouth space called the buccal cavity. Fish use their mouths with jaws or by sucking water and food in; gills sit behind the mouth and help them breathe. Fish teeth can be in many places, like the jaws or the back of the throat.

On land, each group has changed the mouth for its needs. Amphibians often use a sticky tongue to catch insects and swallow whole. Reptiles vary widely: snakes can open their jaws very wide to swallow big prey, while turtles use strong beaks. Birds do not have teeth; their beaks and tongues help them grab and break food. Mammals have a roof and floor in the mouth, a movable tongue, cheeks, salivary glands for wetting food, and different kinds of teeth for cutting and grinding before food moves to the esophagus.

Many animals without backbones, called invertebrates, have a simple gut or a central food space lined with special cells. In creatures like sea anemones, the single opening acts as both mouth and anus—food goes in and waste comes out the same hole. Around the opening, muscles and a ring of tentacles help grab and push food into the pharynx, where digestion begins in a central cavity called the gastrovascular cavity.

Other invertebrates have very different mouthparts. Snails and slugs may use a toothed ribbon called a radula to scrape food. Insects use many parts—mandibles, maxillae, and a labium—to bite, chew, or sip. Sea urchins have a special chewing structure called Aristotle’s lantern.

Thermoregulation means keeping a steady body temperature, and the mouth helps with that. Some animals open their mouths wide to cool off: crocodiles in warm places sit with their mouths open so moisture can evaporate from the mouth lining. Dogs pant to move air and evaporate saliva, and some birds do a quick flutter with the throat area to lose heat without flying away.

Mouths also help animals avoid fights. A wide open mouth, showing teeth, or a bright-colored mouth lining can be a strong warning signal. These displays let animals judge each other and often stop a fight before it starts.

Finally, the mouth is important for sounds and talking. Tongue, lips, teeth, and the space at the back of the throat shape noises. Some animals have other tools too: frogs blow up vocal sacs to make calls, and many birds sing with a special organ called a syrinx.