Amphibia

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mphibiaAmphibia
Digestive System:
1. The digestive system of frog is mainly includes the food catching organs, the alimentary canal and the digestive glands. 2. In the alimentary canal the processes of mastication, digestion and absorption take place, while the digestive glands secrete certain enzymes which bring about the digestion of the ingested food. Alimentary canal:

1. The alimentary canal of the frog is essentially a colied tube of varyihng diameter that extends from one of the body to other. 2. Towards the anterior end it opens through a mouth but at the posterior end it opens through a cloacal aperture as undigested food and reproductive bodies both are removed side by side through this aperture. 3. It consists of the buccal cavity, pharynx, oesophagus, stomach and intestine. Buccal Cavity:

1. The alimentary canal starts with an aperture which is known as mouth opening. 2. Mouth leads into a wide and broad cavity called buccal cavity which lays in between the two jaws- the upper jaw and tha lower jaw. 3. The upper jaw is fixed or immovable, while the lower jaw is hinged and can be freely moved up and down in the vertical plane. 4. The upper jaw bears a row of closely set, small, uniform and hook like pointed maxillary teeth but the lower jaw lacks teeth. 5. Besides maxillary teeth there are two more patches of teeth found one on either side of the median line of the roof of the buccal cavity, they are called vomerine teeth as they are born on the vomer. 6. The teeth are small in size and uniform in structure. 7. They are not used for chewing but prevent the escape of the captured pray. 8. They are curved backwards and attached to the bones instead of being set in sockets. 9. Each tooth is conical in its shape and consists of two parts- the base and the crown. 10. The base forms the roof of the tooth by which it is attached to the jaw. 11. The crown is the free end of tooth separated from the roof by a transverse furrow. 12. The base is formed of bone like substance, while the free end of crown is formed of dentine traversed by numerous fine branching canals leading from the interior of the tooth. 13. The most of the part of the crown is coated with a very hard, resistant, shining white layer of enamel substance. 14. In the interior of each tooth there is a cavity which is called pulp cavity. 15. The buccal cavity in its roof near the vomerine teeth has two openings, the internal or posterior nares connecting with the nostrils through which the respiratory gases pass to and from the buccal cavity during respiration. 16. It also has two opening of Eustachian tubes at the sides of posterior part of the buccal cavity and the glottis which is a median slit in the pharynx behind the tongue that guards the entrance to the lungs. 17. It is always opened during breathing but closes while food is being swallowed. 18. These act as resonators at the time of crocking.

19. The large, thick, fleshy and protractible tongue which is attached in front and free and notched behind. 20. Its upper upper surface bears taste buds in the form of small papillae and mucous glands of which the secretions make the tongue sticky. 21. Neither taste buds not mucous glands produce any digestive enzymes. 22. The tongue can be thrown out and rectracted suddenly to capture and engulf insects. 23. According to hardtop the throwing out of the tongue is brought about by the sudden flowing of squeezed lymph from the lymph sac to another due to muscular contraction but the buccal cavity in which a flat hyoid cartilage is embedded. 24. The buccal cavity narrows behind as the pharynx which opens into oesophagus through gullet. Oesophagus:

1. The gullet leads into a broad tubular part of the alimentary canal called oesophagus. 2. This part of the alimentary canal is very short due to the absence of neck but highly distensible as its...
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