Invertebrates Butterfly tongue Apart from sponges and placozoans, almost all animals have an internal gut cavity which is lined with gastrodermal cells. In less advanced invertebrates such as the sea anemone, the<unk>  also acts as an anus. Circular muscles around the<unk>  are able to relax or contract in order to open or close it. A fringe of tentacles thrusts food into the cavity and it can gape widely enough to accommodate large prey items. Food passes first into a pharynx and digestion occurs extracellularly in the gastrovascular cavity. Annelids have simple tube-like guts and the possession of an anus allows them to separate the digestion of their foodstuffs from the absorption of the nutrients. Many<unk> lluscs have a radula which is used to scrape microscopic particles off surfaces. In invertebrates with hard exoskeletons, various<unk> parts may be involved in feeding behaviour. Insects have a range of<unk> parts suited to their<unk> de of feeding. These include mandibles, maxillae and labium and can be<unk> dified into suitable appendages for chewing, cutting, piercing, sponging and sucking. Decapods have six pairs of<unk>  appendages, one pair of mandibles, two pairs of maxillae and three of maxillipeds. Sea urchins have a set of five sharp calcareous plates which are used as jaws and are known as Aristotle's lantern. Vertebrates In vertebrates, the first part of the digestive system is the buccal cavity, commonly known as the<unk> . The buccal cavity of a fish is separated from the opercular cavity by the gills. Water flows in through the<unk> , passes over the gills and exits via the operculum or gill slits. Nearly all fish have jaws and may seize food with them but<unk> st feed by opening their jaws, expanding their pharynx and sucking in food items. The food may be held or chewed by teeth located in the jaws, on the roof of the<unk> , on the pharynx or on the gill arches. Litoria chloris calling Nearly all amphibians are carnivorous as adults. Many catch their prey by flicking out an elongated tongue with a sticky tip and drawing it back into the<unk>  where they hold the prey with their jaws. They then swallow their food whole without much chewing. They typically have many small hinged pedicellate teeth, the bases of which are attached to the jaws while the crowns break off at intervals and are replaced.<unk> st amphibians have one or two rows of teeth in both jaws but some frogs lack teeth in the lower jaw. In many amphibians there are also vomerine teeth attached to the bone in the roof of the<unk> . The<unk> s of reptiles are largely similar to those of mammals. The crocodilians are the only reptiles to have teeth anchored in sockets in their jaws. They are able to replace each of their approximately 80 teeth up to 50 times during their lives.<unk> st reptiles are either carnivorous or insectivorous but turtles are herbivorous. Lacking teeth that are suitable for efficiently chewing of their food, turtles often have gastroliths in their stomach to further grind the plant material. Snakes have a very flexible lower jaw, the two halves of which are not rigidly attached, and numerous other joints in their skull. These<unk> difications allow them to open their<unk> s wide enough to swallow their prey whole, even if it is wider than they are. Birds do not have teeth, relying instead on other means of gripping and macerating their food. Their beaks have a range of sizes and shapes according to their diet and are composed of elongated mandibles. The upper mandible may have a nasofrontal hinge allowing the beak to open wider than would otherwise be possible. The exterior surface of beaks is composed of a thin, horny sheath of keratin. Nectar feeders such as hummingbirds have specially adapted brushy tongues for sucking up nectar from flowers. In mammals the buccal cavity is typically roofed by the hard and soft palates, floored by the tongue and surrounded by the cheeks, salivary glands, upper and lower teeth. The upper teeth are embedded in the upper jaw and the lower teeth in the lower jaw, which articulates with the temporal bones of the skull. The lips are soft and fleshy folds which shape the entrance into the<unk> . The buccal cavity empties through the pharynx into the oesophagus.
Mouth
Head
Skull
Eye
Earmold
Hand
Labdoor
Nail 