The Dispestive System: Four Types Of The Digestive System

DIGESTIVE SYSTEM
Digestive system is a series of organs involved in the digestion of food eaten, absorption of digested food and expulsion of undigested residue. Digestive system includes alimentary canal and associated glands. The basic plan of digestive system is similar in all vertebrates. But within this basic plan, the specific components vary from one animal to another. The alimentary canal is formed early during embryonic development and is lined with endoderm except mouth and rectum which have ectodermal lining
26. 32) are present in the wall of the buccal funnel and on the tongue. *Tadpole larvae of anurans have serrated epidermal teeth. *True teeth are found in all vertebrates (except cyclostomes, sturgeons, some toads, sirens, turtles and birds). *In fish, amphibians and most reptiles teeth are acrodont, homodont and polyphyodont. *In mammals teeth are thecodont, heterodont and diphyodont. *Teleosts have sharp teeth attached to jaw bones. *In mammals, teeth exhibit morphological variation. Four types of teeth are found in mammals-incisors (cutting), canines (piercing and tearing), premolars and molars (mastication) .ii).Tongue:-*Tongue is a simple crescent shaped elevation in the floor of the oral cavity. *Tongue is non muscular in fish. *Some anurans are tongueless while in others a muscular tongue is present .*In snakes and some lizards tongue is well developed but in turtles and crocodiles tongue is poorly developed. *In birds and mammals tongue is well