The palate (French: Le palais) forms the roof of the mouth cavity proper, and consists of two portions, the anterior or hard palate and the posterior or soft palate.

The hard palate [palatum durum] is continuous in front and laterally with the alveolar processes of the upper jaw, and gives attachment posteriorly to the soft palate. It separates the mouth from the nasal cavity. It is supported by the palatine process of the maxilla and the horizontal part of the palate bone. The oral surface is concave from side to side, and also from before backward. It is covered by a thick, somewhat pale mucosa, which is firmly adherent to the periosteum through the submucosa. The submucosa contains numerous mucous glands [gl. palatinse], similar to those of the lips.

In the median line of the hard palate is a line or ridge, the raphe terminating anteriorly in the small incisive papilla, which corresponds in position to the bony incisive foramen. Anteriorly there occur four to six more or less distinct transverse ridges [plicae palatinae transversae]. Near the posterior margin of the hard palate there is on each side of the raphe a small pit, the foveola palatina, which is variable and inconstant.

The soft palate [palatum molle] separates the posterior portion of the mouth cavity from the nasal part of the pharynx. It is attached to the hard palate anteriorly and to the pharyngeal wall laterally. The posterior portion or velum projects backward and downward into the pharynx. Its free mar- gin presents a median conical projection, the uvula, and splits laterally on each side to form two folds, the palatine arches, between which is located the palatine tonsil. The palatine arches and tonsil will be described later in connection with the pharynx.

Structure of the palate

The soft palate is a fold of mucous membrane enclosing a fibrous aponeurosis, muscles, vessels, and nerves. It is marked in the middle line by a raphe indicating the hue of junction of the two halves from which it was formed.

The posterior layer of the mucous fold which is directed toward the cavity of the pharynx is continuous with the nasal mucous membrane; the anterior layer lies in the posterior boundary of the mouth and is continuous with the mucous membrane of the hard palate. The structure of the mucosa is very similar to that of the lips. Mucous glands are numerous in both layers, but more especially in the anterior, and make up a large portion of the mucosa and sub-mucosa.

The aponeurosis is attached above to the posterior margin of the hard palate; laterally it is continuous with the aponeurotic layer of the pharyngeal wall; below, toward the lower margin of the velum, it gradually disappears. It gives attachment to fibers of the levator veli palatini and the pharyngo-palatinus (palato-pharyngeus) and to the tendon of the tensor veli palatini.

Musclesof the palate

The muscles of the soft palate are described later with those of the pharynx, with which they are closely associated.

Vessels and nerves of the palate

The arterial supply of the hard palate is derived chiefly from the major palatine branches of the internal maxillary. The arteries of the soft palate include:

(1) Ascending palatine of external maxillary (facial);

(2) pharyngeal branches of ascending pharyngeal;

(3) twigs from descending palatine of internal maxillary, which enter the smaller palatine canals, are distributed to the soft palate and tonsils, and communicate with the ascending palatine of the external maxillary (facial) artery;

(4) lingual artery, by twigs from the dorsal branch.

The sensory nerves to the palate are derived chiefly from the fifth through the sphenopalatine ganglion. The hard palate is supplied by the nasopalatine and anterior palatine branches; the soft palate chiefly by the median and posterior palatine branches. The motor nerves will be mentioned later in connection with the muscles.

The development of the palate

The hard and soft palates arise in two ridges of tissue, designated the palate shelves, which develop on the inner surfaces of the maxillary processes. These shelves grow toward the median line, and at the beginning of the third month of fetal life meet beneath the nasal septum, uniting with each other and with the nasal septum, the union taking place from before backward. The incisive foramen indicates the place of meeting of the premaxillary and palate shelves, which closes the primitive communication between the oral and the nasal cavity. A want of union of the palate shelves presents an arrest of development known as cleft-palate. The uvula is similarly formed by the union of the posterior ends of the lateral palate anlages, and a failure to unite may produce a bifid uvula. The transverse palatine ridges are better developed in the infant than in the adult, and may assist in holding the nipple in sucking.

Variations

Cleft-palate and bifid uvula were mentioned above. The transverse palatine ridges are quite variable in number and prominence. On each side of the incisive papilla there is often found a small pit or shallow tube, a vestige of the embryonal incisive canal (Merkel). Sometimes there is instead a single median pit, representing the lower end of the incisive (Stenson's) canal. These pits are remnants of the primitive embryonic communication between mouth and nasal cavities.

Comparative

The palate is absent in fishes and amphibia, the choanae opening directly into the primitive mouth cavity. In some birds, the palate shelves fail to unite, leaving a normal cleft-palate. The incisive (Stenson's) canal remains open permanently in some mammals (e. g., ruminants), bifurcating above and thus placing the mouth cavity in communication with the nasal cavity on each side in the vicinity of Jacobson's organ. The transverse palatine ridges are much better developed among many mammals, especially the carnivora.

From Morris's treatise on anatomy.