The _function_ of the hard palate is mainly mechanical. Acting as a partition between the nasal and buccal cavities, it prevents nasal mucus from falling into the mouth, and, by presenting an opposing surface to the tongue, allows of the production by the latter of the vacuum necessary for suction, and enables the tongue to direct the food towards the alveoli, and to disintegrate soft particles, thus assisting mastication. It is also an accessory to the development of taste by enabling particles to be evenly spread over the back of the tongue. For the production of articulate speech the hard palate is an indispensable factor, and the quality of the voice is much influenced by its contour. The functions of the soft palate are mainly related to the acts of respiration, deglutition, phonation, and articulation. 1. _In respiration._—If the mouth is closed, and the respiration purely nasal, the velum hangs loosely, and allows free passage of air through the posterior nares. If the mouth is open, the velum is raised, and air passes freely through the fauces to or from the larynx. When air passes simultaneously through nose and mouth, the velum hangs in a more or less flaccid condition midway between the two extremes, and sometimes, when absolutely relaxed, vibrates, giving rise to snoring or stertor. 2. _In deglutition._—The passage of food into the nose is prevented by the closure of the posterior nares. This is effected by elevation and tension of the velum, the levator and tensor muscles acting in unison, so that its position becomes almost horizontal. The raised velum meets the posterior wall of the pharynx, which advances as the result of the action of the upper horizontal fibres of the superior constrictor, and the closure is completed on either side by the approximation towards the median line of the posterior pillars of the fauces from the action of the palato-pharyngei muscles contained therein. These, acting from the soft palate as a fixed point, and raising the pharynx to grasp the bolus of food, straighten the walls of the sphincter-like isthmus faucium, and so guide the food as down an inclined plane. The tension of the velum also assists in this guidance. That the above is the action of the palatal structures is proved by the results of their imperfect development or paralysis, _e. g._ in post-diphtheritic paralysis, where the naso-pharyngeal cavities remaining unclosed, food (especially if fluid) regurgitates into the nose.