The palate is a more or less horizontal partition dividing the month from the nasal cavity, and consists of a firm bony plate in front (the hard palate) with a freely moveable membrano-muscular velum behind (the soft palate), which under varying conditions of muscular action can either open or close the communication between the nose and pharynx.

The bony palate forms the vaulted roof of the mouth, the central and posterior parts of which are nearly horizontal; and on all sides, except at the back, it is bounded by the alveolar ridge. Into its formation several bones enter; in the adult skull one usually sees posteriorly a cruciform suture indicating the limits of the superior maxillæ and palate bones; but even in the adult, evidence is forthcoming in the existence of traces of sutures to indicate that the anterior part of the palate is formed independently of the part immediately behind it. Thus Mr. Carless tells me that a cursory examination by him of a few dozen adult skulls picked up at random in the Museum of the College of Surgeons revealed the fact that in quite one half of them traces of sutures could be seen extending outwards from the posterior part of the anterior palatine canal; and a similar examination by him of 40 skulls from the Museum of King’s College of many nations and various ages showed a similar result. In almost all there was distinct evidence of the suture in the median line; in 21, the maxillo-intermaxillary suture was indicated; whilst in 10 skulls, representing the period from infancy to young adult life, both the above were seen in all, and 7 showed traces in addition of a suture placed between them on either side, and which we shall describe hereafter as the endo-mesognathic. Kölliker[34] similarly records that out of 325 adult skulls examined, 96 of them showed definite traces of the maxillo-intermaxillary suture. Albrecht[35] declares that nine tenths of the skulls in the Königsberg and Kiel Museums from children under five years of age reveal the existence of five intermaxillary sutures, proving that there are four separate portions to the so-called intermaxilla. Each portion carries an incisor tooth, and the canine is developed immediately at the junction between the outer portion and the maxilla. Occasionally there are three incisors on each side, the jaw being then called hexaprodontous; the extra tooth is developed from the inner segment of the intermaxilla (or endognathion), the outer segment (or mesognathion) carrying as usual only the lateral incisor. The accompanying illustrations well indicate this arrangement of sutures and teeth (Figs. 26 and 27); the importance of these facts will be emphasized later. All traces of the facial aspect of these sutures disappear quite early in life.

The bony surface of the roof of the mouth is perforated by numerous small foramina for the transmission of the nutrient vessels to the body of the bone, pitted for the lodgment of mucous glands, and grooved longitudinally for the transit of vessels. At the postero-external corners the posterior and accessory palatine canals give entrance to the posterior palatine vessels, and nerves; and anteriorly in the median line is the anterior palatine canal transmitting the naso-palatine vessels and nerves.

The soft palate is a moveable curtain, consisting of a membranous expansion or aponeurosis attached to the posterior extremity of the hard palate by firm fibrous tissue. Incorporated with it are five pairs of muscles, controlling its movements; it is covered by a smooth thin mucous membrane, and terminates posteriorly in the uvula. The arrangement of these muscles is important, not only from their normal physiological functions, but also from their irregular action and effects in cases of cleft palate (Fig. 28). They may be arranged in groups: two, the levator and tensor palati, form a superior group; the azygos uvulæ is intermediate; and the palato-glossus and palato-pharyngeus form an inferior set. Arising from the extremity of the petrous bone, the levator passes downwards, and spreading out below unites with its fellow in the whole length of the median raphe. The tensor arises from the navicular fossa of the internal pterygoid plate, and after being reflected around the hamular process, its action there being assisted by the interposition of a bursa, is attached to the anterior portion of the aponeurosis and to the hinder part of the bony palate. The combined action of these muscles raises and makes tense the velum, and in addition influences the Eustachian tube; but the levator is by far the more important. The azygoi uvulæ muscles arising from the median raphe and spine of the hard palate descend to the tip of that process, and are thus able to regulate its length.

The two descending muscles are placed in the pillars of the fauces, forming the lateral prolongations of the velum, and the tonsils lie in a recess between them. The palato-glossi arising from the tongue ascend in the anterior pillars of the fauces, and spreading out on the anterior surface of the velum unite in the median raphe. The palato-pharyngei start from the median raphe in two lamellæ enclosing the termination of the levator muscle; they descend in the posterior pillars of the fauces, and being attached to the pharyngeal wall between the superior and middle constrictors, by their contraction assist in raising the pharynx during deglutition.

The nervous supply of these muscles requires little notice here; suffice it that the superior set and the azygos are supplied by the facial nerve, the inferior set from the pharyngeal plexus.

The mucous membrane of the hard palate is of the usual oral type, and only differs from that of the rest of the mouth in its close attachment to the periosteum, from which in fact it is almost impossible to separate it. It is thick, dense, rather pale and much corrugated, especially in front and at the sides, whilst behind over the velum it is smoother and thinner. In it are many small glands (palatine glands) which extend down to the periosteum. In the median line is a well-marked raphe, extending anteriorly to a prominence indicating the position of the anterior palatine canal. The rugose condition of the membrane over the hard palate is not seen in young children; it supervenes later in life.

The vascular supply of the palate is free and abundant, a circumstance which is of the greatest surgical importance in that it permits of the free detachment of the soft structures from the hard by long lateral incisions, and the necessary manipulation of these in uranoplastic operations without any fear of loss of vitality, provided that the patient’s health and constitution are tolerably sound, and that sufficient pedicle is left in front and behind.

The mucous membrane of the hard palate derives its blood supply from two of the terminal branches of the internal maxillary artery. The naso-palatine descend through the anterior palatine canal, and entering the palate at the incisive foramen (foramina of Stenson) assist in supplying the anterior portion, anastomosing with the terminations of the more important posterior or descending palatine, which find their way to the palate from the spheno-maxillary fossæ through the posterior palatine canals. Each of the latter arteries on reaching the palate sends branches to the velum and tonsils, and its main twig runs onwards in a groove of the bone to supply the mucous membrane and glands of the hard palate and gums. Its usual position is parallel to the alveolar border, and about three quarters of an inch from it; but this varies considerably. The artery can often be felt pulsating as it emerges from the bone, and is very likely to be divided in the lateral incisions made during the operation of uranoplasty; but the knife should be carried external to it, if possible, so that the trunk of the vessel may be preserved in the flap. The bony palate derives its blood supply not only from its lower surface but also from its upper, and hence detachment of the inferior periosteal covering does not lead to death of the bone. The soft palate derives its blood from three sources, viz. the ascending palatine of the facial, the ascending pharyngeal, and the posterior palatine of the internal maxillary. The two former reach it through the sinus of Morgagni, i. e. over the upper border of the superior constrictor muscle, forming loops of anastomosis on its posterior aspect with similar branches on the opposite side; the last supplies the anterior palatal surface.

The normal shape of the palate is a regular arch, bounded laterally by the gums and alveoli into which the teeth are implanted so as to describe a parabolic curve, being normally uninterrupted at any spot by spaces or diastemata. The height and curvature of the palate vary considerably in different individuals, not only from inherited peculiarities, but also from acquired conditions dependent on the teeth. A person with a good set of sound teeth will probably own a regular well-formed palate; whilst if sundry of the upper permanent teeth are lost during the stage of adolescence, the palate is likely to become high and narrow from the falling in of the jaw. This is especially the case if the incisor teeth are lost.

The shape of the palate in a child of two years does not differ so markedly as one would at first expect from that of an adult except in length, and the reason for this is plainly the existence in the latter of three additional teeth on each side. Its increase in length is from 20 to 30 millimetres, whilst its breadth is only augmented by 10 to 15 mm., and this mainly posteriorly. When once the permanent incisors, canines, and premolars are developed, the anterior portion of the palate alters but little in shape, unless any of these teeth be lost, and the gaps not artificially maintained.

Dr. Ehrmann[36] states that the alveolar border in front of the canine teeth forms a nearly regular semicircle, with a posterior transverse diameter of 22-26 mm.; thence the alveoli diverge regularly, adding to the diameter about 2-4 mm. for each tooth. He gives the following measurements as the mean of many observations:

Oakley Coles[37] has carefully investigated the size of the palate in several series of skulls in the Museum of the College of Surgeons, and gives the results as follows:

Of 34 adult skulls of European origin, the average length was 49 mm., the average width at the second bicuspid was 35 mm., and the average height from the margins of the alveoli 9 mm.

Of 32 adult skulls of mixed races, the average length was 54 mm., the width 35 mm., and the height 12 mm.

The frequent association of inherited mental and nervous weakness with a high arched palate is now a well-established clinical fact. Thus Savage states that in “Genetous Idiocy” (i. e. idiocy which starts in fœtal life, and cannot be traced to any specific disease) the palate is usually keel-shaped, the molar teeth being closely approximated; they are also late in appearing and deficient in number. “Although this kind of palate may be present in healthy individuals or in those suffering from ordinary insanity, if it be associated with weak-mindedness or moral peculiarities in youth I believe one is justified in saying that the tendency to moral or intellectual deficiency is congenital.”[38] Only recently Dr. F. Warner has reported[39] to the Psychological Section of the British Medical Association the results of an investigation as to the occurrence of deformities amongst school children, and their relationship to defective vital and mental conditions. Out of 5344 children examined, physical deformity was noted in 399 cases, and of these 274 were boys and 125 girls, i. e. in the proportion 9·8 per cent. and 5 per cent. respectively. It was found that of these 25 per cent. exhibited evidences of low nutrition, 36 per cent. evidences of nervous weakness, and 31 per cent. of mental dulness. 117 cases were noted of deformity of the palate, 77 boys and 40 girls; and of these 35 per cent. gave signs of low nutrition, 39 per cent. of nerve weakness, and 35 per cent. of mental dulness. These defects were more marked and more frequent in the pauper than in the elementary public schools, in the proportion of 4·2 to 2·2. As to the character of the malformations, the following are the numerical statistics: In 105 cases, the palate was arched, narrow, high or vaulted; in 8, it was 𝖵-shaped; in 4 it was of the flat type.

Dr. Langdon Down[40] had previously noticed and pointed out this frequent relationship, remarking that as the result of a large number of careful measurements of the mouths of the congenitally feeble-minded and of intelligent persons of the same age, he found with few exceptions a marked diminution in the transverse measurement between the posterior bicuspids, resulting in an inordinate vaulting of the palate. There was often noticed an actual deficiency in the bony structures of the posterior part of the hard palate, causing the velum to hang down abnormally, interfering with phonation.

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.

3. In phonation and articulation.—The soft palate is here of considerable importance, inasmuch as it is needed to cut off the naso-pharynx and nasal cavities from the oral pharynx. When defective or paralysed, a certain amount of nasal resonance is imparted to the voice, which, however, is less noticeable during vocalisation than in articulation. For the production of clear normal voice-sounds it is essential that the separation between nose and mouth should be absolute, except for the sounds m, n, and ng. The American twang is probably due to a slight relaxation of the soft palate, permitting a small percentage of voice-sounds to pass through the nose. Dr. N. W. Kingsley[41] has recently published some excellent diagrams illustrating the position of these parts during the production of definite sounds, and for all, except those mentioned above, the velum is horizontal, and in contact with the posterior pharyngeal wall.