Pigeon - Digestive system
The two jaws of the mouth are modified into beak. Both the jaws are devoid of teeth. The mouth leads into the buccal cavity. The floor of the buccal cavity is provided with a narrow, triangular tongue. It has a horny covering and is provided with sensory papillae. The buccal cavity narrows behind into the Pharynx. The salivary glands are absent in the buccal cavity. Three pairs of buccal glands are present in the mouth. Their secretion is mainly mucous.
The alimentary canal proper starts from the Pharynx. The Pharynx leads into a long oesophagus that runs back through the neck. At the base of the neck region, it enlarges into a thin walled, distensible sac known as crop containing mucous glands. It serves as a store house for the food. The crop is followed by the stomach. The stomach is divisible into two parts, the anterior tubular proventriculus containing gastric glands and a posterior laterally compressed gizzard. The gizzard has a thick muscular wall and a horny inner lining. Its cavity is small and contains small stones which are helpful to grind the food. Thus the gizzard acts as a grinding mill. This type of arrangement is necessary because of the absence of teeth in the buccal cavity. The intestine arises from the right side of the gizzard. It is divisible into an anterior U- shaped duodenum, and a posterior long coiled ileum. The ileum enlarges posteriorly into a short rectum or large intestine. Anteriorly, the rectum bears a pair of small rectal caeca. The rectum opens to the exte-rior by the cloaca.
Internally the cloaca is divided into three chambers, the anterior coprodaeum, the middle urodaeum and the posterior proctodaeum. The rectum opens into the coprodaem. The urinogenital ducts open into the urodaem. The proctodaem opens to the exterior by a transverse slit like
aperture called cloaca. At the proctodacum, there is a dorsal glandular sac known as Bursa of Fabricii. Its function is unknown.
The digestive glands associated with the alimentary canal are the liver and the pancreas. The liver is bilobed with a large right and a small left lobe. It is devoid of gall bladder. There are two bile ducts. They are forms one from each lobe. They open into the duodenum independently. The pancreas lies between the two limbs of the duodenum. It has three ducts, all opening into the distal limb of the duodenum.
Sub phylum - Vertebrata
Class - Aves
Order - Columbiformes
Type - Columba livia
Birds are easily recongnised group of vertebrates. In birds every part of the body is modified to suit their aerial mode of life. Birds possess feathers, beak and feet modified in relation to their aerial life.
The Pigeons are flying birds(carinate). They are known both as wild and domesticated forms. The Pigeons are seen both in tropical and temperate zones. About 10 species of Pigeons are found in India. The pigeons fly in flocks and roost together. The domestic pigeons have many varieties, namely panter, fantail and tumblers. They differ in size, colouration and feather ar-rangement. All of them are, however, descendants of the rock pigeon-columba livia.
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