Oral glands

Glands located in the mouth that secrete fluids to moisten and lubricate the mouth and food and may initiate digestive activity, and that may perform other specialized functions. Fishes and aquatic amphibians have only solitary mucus-secreting cells in the epithelium of the mouth cavity. Multicellular glands first appeared in land animals to keep the mouth moist and make food easier to swallow. Some glands of terrestrial amphibians have a lubricative secretion; others serve to make the tongue sticky for use in catching insects. Some frogs secrete a serous fluid that contains ptyalin, a digestive enzyme. The oral glands of reptiles are much the same, but are more distinctly grouped. In poisonous snakes and the single poisonous lizard, the Gila monster, certain oral glands of the serous type are modified to form venom. Also many of the lizards have glands that are mixed in character, containing both mucous and serous cells. Oral glands are poorly developed in crocodilians and sea turtles. Birds bolt their food, yet graineaters have numerous glands, some of which secrete ptyalin.

All mammals except aquatic forms are well supplied with oral glands. There are numerous small glands, such as the labial glands of the lips, buccal glands of the cheeks, lingual glands of the tongue, and palatine glands of the palate. Besides these, there are larger paired sets in mammals that are quite constant from species to species and are commonly designated as salivary glands. The parotid gland, near each ear, discharges into the vestibule. The submaxillary or submandibular gland lies along the posterior part of the lower jaw; its duct opens well forward under the tongue. The sublingual gland lies in the floor of the mouth. It is really a group of glands, each with its duct. See also Gland.