Calotes compare enzymes in the digestive system a poikilothermic and terrestrial lizard. Columba and Oryctolagus are warm blooded animals. Columba is adapted for mode of life-bird. The digestive system consists of alimentary canal and its associated digestive glands. The living of the alimentary canal is mostly endodermal in origin being derived from the wall of the archenteron.
Distinc’ salivary glands secreting enzymes are present only in mammals. The secretions of which serve primarily to keep the mouth moist and secondarily to facilitate the movements of the tongue. The other connected with the midgut and arising as out growth are the liver and pancreas. Mouth is a wide, slit present at the anterior end of head. Mouth is terminal, slitlike aperture bounded by horny Jaws. Mouth is sub-terminal, cleft bounded bv mobile, fleshy lips. Buccal cavity is a narrow gap. Buccal cavity is a spacious chamber andits space between lips and the teeth is called vestibule.
This receives the mouth opening. On both jaws teet are present, polyphyodont homodont teeth arranged in a single row on each jaw. Teeth are not useful for mastication. Jaws are modified into tooth less beak. Teeth are diphyodont, heterodont and thecodont.
These are arranged in a single row on each Jaw. Tongue is attached posteriorly to the floor describe the general structure of enzymes buccal cavity and is free anteriorly. Tongue is narrow triangular and fleshy. Its surface is covered with horny material and bears thorn-like projections which carry taste buds and mucous glands.
It can be protruded out. Its surface is rugose being covered with numerous papillae along with taste buds. A pair of internal nostrils open into the roof of the buccal cavity anteriorly. A bony palate is wanting in birds but a pair of palatal folds and palatal groove between the two folds are present. Internal nostrils are located dorsal to the palatal folds.
The nasal passages are separated from the buccal cavity by a bony palate. The internal nostrils open into the pharynx nearer to glottis. A bony palate is present covering the roof of the buccal cavity. A bony palate is absent. But soft palate is formed of two membranous folds. The palate is differentiated into anterior bony hard palate and a soft palate is formed of connective tissue. Unicellular mucous glands are present and keep the buccal cavity always wet. Unicellular mucous glands are absent in the epithelium of bucco-pharyngeal region. Uni cellular mucous glands are absent.
But multi cellular serous glands are present. But labial glands are open at the lips which do not play any role in digestion. Salivary glands which open into the buccal cavity are lingual, mandibular, maxillary, cricoary tenoid, palatinal and sphenopalatinal glands. The multi cellular salaivary glands are four pairs. They are Infra orbital, parotid, sublingual and sub-maxillary glands. On the roof of pharynx near the junction of two jaws a pair of function of enzymes in living things is called Eustachian apertures. Pharynx is not sharply demarcated from the buccal cavity.