palate(redirected from Secondary palate)
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palate(păl`ĭt), roof of the mouth. The front part, known as the hard palate, formed by the upper maxillary bones and the palatine bones, separates the mouth from the nasal cavity. It is composed of a bone plate covered with a layer of mucous membrane tissue. The back portion, or soft palate, consists of muscular tissue and mucous membrane forming a partial partition between the mouth and the throat. A small conelike projection, the uvula, hangs from the middle of the soft palate in humans. The soft palate and uvula move upward during swallowing or sucking, preventing food from entering the nasopharynx. In mammals other than humans, the soft palate overlaps the larynx during swallowing so as to prevent entry of foreign substances into the respiratory tract. Both the hard and soft portions of the palate are lined with mucous membrane containing numerous glands that lubricate the mouth and throat. If the sides of the bony palate fail to come together during embryonic development an opening, or cleft, remains along the midline. This condition, known as cleft palate, can be repaired surgically in early infancy. See digestive systemdigestive system,
in the animal kingdom, a group of organs functioning in digestion and assimilation of food and elimination of wastes. Virtually all animals have a digestive system. In the vertebrates (phylum Chordata, subphylum Vertebrata) the digestive system is very complex.
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the roof of the oral cavity in vertebrate animals and man.
In petromyzons, Myxine, and cartilaginous fish, the palate is formed from the base of the chondrocranium; in bony fish and terrestrial vertebrates with secondary jaws, it is formed from the bones that originate in the base of the skull and at the site of the palatoquadrate cartilage. In some fish (Dipnoi and Crossop-terygii) and terrestrial vertebrates, the anterior section of the palate has primary choanae, or internal nares. In a number of reptiles (Testudinata, crocodiles, and Pelycosauria) and in mammals, there is a secondary hard palate, formed from the membrane bones; it divides the oral cavity from the nasopharyngeal passages, which open into the pharynx through the secondary choanae. The secondary palate in reptiles and mammals prevents the entry of food into the air passages and the disruption of breathing; in crocodiles it facilitates normal respiration when food is captured in the water. The appearance of a secondary bony palate in mammals strengthened the posterior sections of the upper jaw, which was one of the conditions for the development of true molars. The hard palate in mammals gradually develops into the muscular membrane known as the soft palate, which delineates the fauces—the opening into the pharynx—superiorly and laterally.
In man the palate is a solid membrane that divides the oral and nasal cavities. It consists of the bony palate (part of the skeleton of the facial cranium), which is covered with a mucous membrane on each side of the cavities. The bony palate is formed from the palatine processes of the left and right maxillae and the horizontal membranes of the palatine bones, which are united by the sagittal and transverse sutures. The superior surface of the hard palate is almost flat—it serves as the floor of the nasal cavity; the inferior surface of the hard palate faces the oral cavity and has a concave, domelike shape. The soft palate, which consists of mucous membrane with submucosal tissue and a muscular layer with fatty tissue, is a continuation posteriorly of the hard palate. The mucous membrane on the side of the oral cavity is lined with multilayered epithelium, and on the side of the nasal cavity with ciliated epithelium. The hard and soft palates together constitute the superior wall of the oral cavity.
When there is disturbance of embryo formation, defects in the development of the palate may arise, including cleft palate.