Roof of Mouth
The roof of the mouth, or palate, forms the superior and posterosuperior boundaries of the “oral cavity proper,” which it separates from the nasal cavity and nasopharynx. The region of approximately the anterior two thirds of the palate has a bony framework and is, therefore, the hard palate; the posterior third is the soft palate. The palate is variably arched both anteroposteriorly and transversely, the transverse curve being more pronounced in the hard palate.
The bony framework of the hard palate is formed by the palatine processes of the two maxillae and the horizontal processes of the two palatine bones that meet in the midline. These bony structures also form the floor of the nasal cavity, and this common bony wall is traversed near the midline anteriorly by the incisive canals, which transmit blood vessels and nerves between the mucous membrane of the nose and the mucous membrane of the palate. In a posterolateral position at each side of the bony palate are the greater and lesser palatine foramina for the transmission of the greater and lesser palatine vessels and nerves. The oral surface of the bony palate is covered by mucoperiosteum (mucous membrane and periosteum fused together), which exhibits a faint midline ridge, the palatine raphe, at the anterior end of which is a slight elevation called the incisive papilla. Running laterally from the anterior part of the raphe are about six transverse ridges, the transverse plicae.
Anteriorly, the soft palate is continuous with the hard palate and ends posteroinferiorly in a free margin, which forms an arch, with the palatoglossal and palatopharyngeal folds on each side as its pillars. The uvula, greatly variable as to length and shape, is a projection that hangs inferiorly from the free margin of the soft palate on the midline. The framework of the soft palate is formed by a strong, thin, fibrous sheet, known as the palatine aponeurosis, which is partially formed by the tendons of the tensor veli palatini muscles. In addition to the aponeurosis, the thickness of the soft palate is made up of the palatine muscles, many mucous glands on the oral side, and a mucous membrane on both the oral and pharyngeal surfaces. The mass of glands extends forward onto the hard palate as far anteriorly as a line between the canine teeth.
The muscles of the soft palate can be briefly described as follows: (1) the levator veli palatini arises from the posteromedial side of the cartilaginous portion of the auditory tube and the adjacent inferior surface of the petrous portion of the temporal bone. Its anterior fibers insert in the palatine aponeurosis, and the posterior ones are continuous with those of the opposite side; (2) the tensor veli palatini arises from the anterolateral side of the cartilaginous portion of the auditory tube and the adjacent angular spine and the scaphoid fossa of the sphenoid bone. Its tendon passes around the pterygoid hamulus, which acts as a pulley, and then spreads out into the palatine aponeurosis; (3) the uvular muscle arises from the posterior nasal spine and palatine aponeurosis, and unites with its counterpart on the other side to end in the mucous membrane of the uvula; (4) the palatoglossus muscle runs from the soft palate to the side of the tongue; and (5) the palatopharyngeus muscle runs from the soft palate inferiorly into the pharyngeal wall. These muscles are supplied by vagus nerve fibers, probably from the cranial part of the spinal accessory nerve, except for the tensor veli palatini, which is supplied by the mandibular branch of the trigeminal nerve.
By means of the actions of the described muscles, the soft palate can be positioned as necessary for swallowing, breathing, and phonation. It can be brought into contact with the dorsum of the tongue and it can be brought up against the wall of the pharynx, which is important in closing off the asopharynx from the oropharynx during swallowing.