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widens out, and terminates opposite a slight projection-the labial tubercle-on the free edge of the upper lip. This tubercle is particularly well developed in children, and is chiefly responsible for the characteristic curve of the rima oris. The lower lip is usually longer and more movable than the upper lip.
For the manner in which the various muscles enter into the formation of the lip, see section on the Muscles (pages 450 to 451).
The lips include within them the greater part of the orbicularis oris muscle, which surrounds the aperture of the mouth, and in each lip the following series of structures can be recognised from the external to the internal surface:-(1) The skin, which is closely beset with hairs, small and fine in the child and female, long and stout in the adult male. (2) A layer of fatty superficial fascia continuous with the fascia of the face generally. (3) The orbicularis oris muscle, continuous at its periphery with the various muscles converging towards the mouth. A number of its fibres, or those of the muscles joining it, pass through the superficial fascia and are attached to the skin, thus establishing a close connexion between the skin and the muscle. (4) The submucous tissue, which is occupied by an almost continuous layer of racemose glands—the labial glands. These open into the vestibule, and their secretion is said to be mucous. (5) The mucous membrane of the mouth, covered by stratified squamous epithelium. Between the orbicularis and mucous membrane, but nearer to the former, that is, in the deeper part of the submucosa, the labial artery is found, a short distance from the free margin of the lip, running to meet its fellow of the opposite side.
The free margin of the lip is covered with a dry and otherwise modified mucous membrane. It begins where the integument changes colour at the outer edge of the lip, and ends posteriorly just behind the line along which the two lips meet when closed, where it passes into the ordinary moist mucous membrane of the vestibule. It presents numerous simple vascular papillæ, and its nerves terminate in special end organs, hence the acute sensitiveness of this part. In the child, at birth, the margin of the lip is divided by a very pronounced groove or fissure into an outer and an inner zone, differing considerably in their appearance.
When the tongue is pressed firmly against the back of the lips and moved about, the labial glands can be distinctly felt through the mucous membrane, giving the impression of a knobby or irregular surface. The glands, which are about the size of hemp-seeds and can be readily displayed by removing the mucous membrane, are more numerous in the lower than in the upper lip. Stoppage of their ducts, with the resulting distension of the glands, gives rise to mucous cysts," a well-known pathological condition.
Blood-vessels, Nerves, and Lymph-vessels.-The lips receive a free blood supply, the lower lip from the inferior labial, and the upper from the superior labial branches of the external maxillary artery.
The sensory nerve supply of the lips is derived from the trigeminal nerve, that of the upper through the infra-orbital branch of the maxillary division, and that of the lower from the mental branch of the inferior alveolar branch of the mandibular division, while the buccinator branch of the mandibular division supplies the region of the angle. The lymph-vessels of the upper lip pass with the external maxillary artery to the submaxillary lymph-glands lying in the submaxillary triangle, while those from the lower lip pass in part to the same glands, and in part to the submental glands lying on the mylo-hyoid muscles, above the hyoid bone.
Bucca. The cheeks resemble the lips in structure, being formed of corresponding layers, but the place of the orbicularis oris muscle is taken by the buccinator muscle. They are covered externally by the skin and internally by the mucous membrane. Under the skin lies the fatty superficial fascia of the face, through which the parotid duct (O.T. Stenson's duct) runs inwards to pierce the buccinator. Here too are placed some of the muscles of facial expression. Near the end of the duct are found four or five mucous glands, as large as hemp-seeds. These are known as the molar glands; their ducts pierce the cheek and open into the vestibule. Beneath the superficial fascia lies the buccinator muscle, covered by the thin bucco-pharyngeal fascia. Deeper still is the submucosa, which, like that of the lips, contains numerous racemose buccal glands. finally the mucous membrane is reached (Fig. 876).
An important constituent of the cheek of the infant is the corpus adiposum bucca (O.T. sucking pad), an encapsuled mass of fat, distinct from the surrounding superficial fascia, which lies on the outer side of the buccinator, and passes backwards into the large recess between that muscle and the overlying anterior part of the masseter. This fatty mass, which is relatively more
developed in the child than in the adult, strengthens the cheek, and helps it to resist the effects of atmospheric pressure during the act of sucking. In the adult the remains of the pad can be distinctly made out under the anterior border of the masseter.
Some small superficial lymph-glands lie on the superficial surface of the buccinator, communicating with the vessels of the lips, while their efferent vessels pass onwards towards the parotid region.
Palatum. The palate forms the roof of the mouth, and separates the mouth from the nasal cavities and nasal part of the pharynx.
It is not confined to the mouth, but extends backwards also into the cavity of the pharynx, forming the division between the oral and the nasal parts of the pharynx. It terminates behind in a free conical projection, the uvula. It consists of two distinct portions, an anterior, forming the anterior two-thirds, which has a bony foundation (palatine processes of the maxillæ and the horizontal parts of the palatine bones), and a posterior, forming the posterior third, with a fibrous basis; and they are termed the hard and the soft palate, respectively. The palate is arched antero-posteriorly, and also transversely. The latter curvature is the more pronounced in the hard palate, but the shape and curvature of this portion depend upon the configuration of its bony foundation.
The hard palate is, on the whole, horizontal in direction, both transversely and anteroposteriorly. The soft palate is, on the other hand, during rest, as, for instance, in quiet nasal breathing, very oblique in direction, and it shuts off the mouth from the nasal and largely from the oral parts of the pharynx. When, however, the soft palate is raised by the action of its muscles, it more nearly continues backwards the plane of the hard palate, and it projects across the cavity of the pharynx, forming a nearly complete partition between the oral and the nasal parts of the pharynx. In this position it prevents food from passing upwards into the nasal part of the pharynx and nose.
Traversing the middle of the palate is seen a faint median ridge or raphe (Fig. 877), indicating its original development from two halves. This raphe is continued posteriorly along the soft palate to the base of the uvula, and in front it ends in a slight elevation, the papilla palatina (O.T. incisive pad). From the anterior end of the raphe a series of transverse ridges of mucous membrane, about six in number, run laterally, just behind the incisor teeth; they are known as the plica palatine, and are composed of dense fibrous tissue. Sometimes a small pit, which will admit the point of a pin, is seen, on each side, immediately posterior to the central incisor teeth, and about 2 mm. from the median plane. These pits correspond to the inferior openings of the incisive canals, with which they are occasionally continuous.
Palatum Durum.-The hard palate consists of a horizontal plate formed by the palatine processes of the maxillæ and the horizontal parts of the palatine bones,
covered on each surface, superiorand inferior, by periosteum. The periosteum of the inferior surface is thick, and is in turn covered by a quantity o
Dentes præmolares dense fibrous tissue firmly united both to the periosteum and to the mucous membrane. This dense tissue contains in its posterior half a large number of racemose palatine glands, and it also contains the larger nerves and blood vessels of the palate. The mucous mem brane covering the superior surface is largely ciliated in character, and forms the floor of the nasal cavity, while that on the inferior surface is a stratified squamous epi
SEEN FROM BELOW.
Palatum Molle. The soft palate is attached anteriorly to the posterior margin of the hard palate. Its lower and posterior margin is free, and forms an arch, extending from one side of the pharynx to the other, but the arch is interrupted
in the centre by the conical projection of varying size, called the uvula, which hangs down from its inferior margin. Laterally the soft palate is intimately connected on each side with two prominent folds, called the palatine arches. The exact relationSe ship of the soft palate to these is as follows. The free posterior margin of the soft palate passes into the pharyngo-palatine arch (O.T. posterior pillar of the fauces), which passes downwards for some distance on the side wall of the pharynx.
The glosso-palatine arch (O.T. anterior pillar of the fauces), on the other hand, b passes below into the side of the tongue. Traced upwards, it runs on to the inferior surface of the soft palate, and is continuous with the margin of the uvula.
The two palatine arches on each side are 7-8 mm. apart, and on the side wall, between each pair, there is a fossa or depression which is occupied in part by the palatine tonsil. This region belongs properly to the pharynx, and will be described in detail when that part is dealt with, but at the present stage the relation of this fossa of the tonsil to the soft palate should be carefully noticed.
The superior surface of the soft palate forms a continuation backwards and downwards of the floor of the nasal cavity, and constitutes the floor of the nasal part of the pharynx. It is covered by a prolongation of the nasal mucous membrane, partly ciliated in character. The inferior surface is arched, and forms the backward prolongation of the roof of the mouth.
In the foetus the whole of the epithelial covering of the soft palate is ciliated, but after birth the ciliated epithelium is largely replaced by stratified squamous epithelium, except at the margin of the palate.
Structure. The framework of the soft palate is formed of a strong fibrous sheet, called the palatine aponeurosis. To it several muscles are attached. These structures, together with fibrous tissue, gland-vessels, and nerves, are covered by mucous membrane on each surface.
The palatine aponeurosis, which is confined to the anterior part of the soft palate, is in the form of a thin flat sheet, constituting a common tendon for the palatine muscles which are attached to (or blended with) its posterior margin. Its anterior margin is united to the posterior edge of the horizontal parts of the palatine bones. With the exception of the aponeurosis of the tensor veli palatini which passes into its lateral part, the muscles do not, as a rule, reach further forwards than to within 8 or 10 mm. of the posterior edge of the hard palate.
The muscles entering into the formation of the soft palate are the mm. pharyngo-palatini, uvulæ, levatores veli palatini, tensores veli palatini, and glossopalatini. For the details of the attachments and arrangement of these muscles, see p. 466.
The anterior part of the soft palate for 8 or 10 mm. (in.) contains practically no muscular fibres; it is composed of the palatine aponeurosis, covered by an extremely thick layer of glands on the inferior surface and by mucous membrane on both surfaces. This anterior portion is much less movable than the rest of the soft palate, and forms a relatively horizontal continuation backwards of the hard palate, stretching across between the two medial pterygoid laminæ. It is upon this portion chiefly that the tensor veli palatini muscles act. The posterior and larger part contains muscular fibres in abundance, slopes strongly downwards, and is freely movable, being the portion upon which the remaining palatine muscles act.
The mucous membrane of the inferior surface of the palate, which is covered by stratified squamous epithelium, is firmer and more closely adherent in front, near the rugæ, than behind, near the soft palate.
Mucous glands, the orifices of which can be seen as dots with the naked eye, are extremely abundant in the soft palate, and in the posterior half of the hard palate, except near the raphe. They are wanting in the anterior part of the palate, where the mucous membrane is particularly dense.
The plicæ palatine (which correspond to more strongly developed ridges in carnivora, etc.) are very well marked in the child at birth, although, perhaps, relatively less distinct in the fœtus of five or six months; in old age they become more or less obliterated and irregular. At birth, also, and in the foetus, the incisive pad at the anterior end of the raphe is continued over the edge of the gum into the frenulum of the upper lip.
The uvula, already referred to, is a conical projection, very variable in length, which is continued downwards and backwards from the middle of the posterior border of the soft palate. It is composed chiefly of a mass of racemose glands and connective tissue covered by mucous membrane, and containing a slender prolongation of the uvular muscle in its upper part.
The vessels of the palate are:
(1) Branches from the descending palatine artery, a branch of the internal maxillary artery. Of these, some small vessels, the lesser palatine arteries, emerge from the foramina palatina
minora, and are distributed to the palatine tonsil and palate, and anastomose with branches of the ascending pharyngeal artery.
The largest branch, greater palatine artery, emerges through the foramen palatinum majus, and runs forwards over the lateral margin of the hard palate, about 4 in. from the alveolar margin, as far as to the foramen incisivum, where it anastomoses with the naso-palatine artery.
(2) Posterior nasal septal artery, a small vessel which enters through the foramen incisivum.
(3) Ascending palatine artery, from the external maxillary, which anastomoses by a ramus tonsillaris with the descending palatine.
(4) Branches from the ascending pharyngeal artery, which enter the soft palate.
(5) Branches from the rami dorsales linguæ of the lingual artery, which pass in the glossopalatine fold to the palatine tonsil and soft palate.
The nerves are all derived from branches from the spheno-palatine ganglion.
(1) Nervi palatini. The most important of these is the nervus palatinus anterior, which passes through the foramen palatinum majus, and divides in the roof of the mouth into branches which run in grooves on the hard palate, and extend forwards nearly to the incisor teeth.
The others are the nn. palatini medius and posterior, which emerge from the foramina palatina minora, and are distributed to the hard and soft palate.
(2) N. nasopalatinus (Scarpa). This nerve sends branches to the palate through the foramen incisivum, which join with branches from the anterior palatine nerves.
For the motor nerves to the muscles of the soft palate, see p. 467.
The lymph-vessels of the palate pass lateral to the tonsil and the isthmus of the fauces to the upper deep cervical lymph-glands.
Isthmus Faucium.-The isthmus of the fauces is the aperture through which the mouth communicates with the oral part of the pharynx (Fig. 878). It is
bounded at the sides by the glossopalatine arches, above by the inferior surface of the soft palate, and below by the dorsum of the tongue; in width it corresponds pretty closely to the cavity of the mouth.
The arcus glosso - palatini (O.T. anterior pillars of the fauces) are two prominent folds of mucous membrane which bound the isthmus of the fauces on each side (Fig. 878). Each contains a glosso-palatine muscle in its interior. They are continuous above with the inferior surface of the soft palate, a little way (about 8 mm.) anterior to its free edge, and near the base of the uvula, and they pass downwards and slightly anteriorly to join the side of the tongue a little behind its middle.
The arcus pharyngo-palatini (O.T. posterior palatine arches) are two verti cal folds of mucous membrane which pass from the soft palate to the side wall of the pharynx. Each contains a muscle, the pharyngo-palatinus. The pharyngo-palatine arches are de
scribed in connexion with the palatine tonsil (p. 1145).
Gingivæ.-The gums are composed of the red firm tissue which covers the alveolar borders of the maxilla and mandible, and surrounds the necks of the teeth. In structure they consist of dense fibrous tissue, inseparably united to the periosteum, covered by mucous membrane. They are richly supplied with blood-vessels, but sparsely with nerves, and are covered by stratified squamous epithelium. Around the neck-or more correctly the base of the crown of each tooth, the gum forms a free overlapping collar, and at this part Darticularly it is closely studded with small papillæ, visible to the naked eye. In thickness it usually measures from 1 to 2 mm.
Each tooth is a calcified papilla of the mucous membrane of the mouth, and consists, like that membrane, of two chief portions-namely, the substantia eburnea or ivory (O.T. dentine) derived from the connective tissue, and the substantia adamantina or adamant (O.T. enamel) from the epithelial layer of the mucous membrane. The substantia eburnea constitutes the chief mass of the tooth, whilst the substantia adamantina forms a cap for the portion which projects above the gum. There is also found in the teeth another special tissue-the substantia ossea (O.T. cement), a form of modified bone-encasing the roots, which are formed chiefly of substantia eburnea.
Both ivory and adamant, but particularly the latter, are the hardest and most resistant structures in the body, and are thus specially
fitted for the func- 2nd permanent
Dentes Decidui and Dentes Permanentes (Deciduous and permanent teeth). The mouth of the infant at birth contains no
teeth, although a Mandibular
number, partly de
beneath the gum.
Some six months FIG. 879.-TEETH OF A CHILD OVER SEVEN YEARS OLD (modified from Testut).
later, teeth begin to appear, and by the end of the second year a set, known as the deciduous teeth (O.T. milk teeth), twenty in number, has been "cut." Then follows a pause of about four years, during which no visible change takes
By the removal of the bony outer wall of the alveoli, the roots of the teeth which have been erupted, and the permanent teeth which are still embedded in the mandible and maxilla, have been exposed. The deciduous teeth are coloured blue, the permanent teeth yellow. It will be seen that the first permanent molars have appeared, the central and lateral deciduous incisors have been replaced by the corresponding permanent teeth in the maxilla, but the deciduous canine and molars have not yet been shed. In the mandible the central deciduous incisor has been replaced by the permanent central; the lateral has not yet been shed, but its permanent successor is making its way up to the surface on its lingual side. In addition, the canine and two molars of the deciduous set persist. The position of the crowns of the permanent teeth between the roots of the deciduous molars, and the deep situation occupied by the permanent canines, should be noted. Observe also the absorption of the root of the lower lateral incisor.
place in the mouth, although in reality an active preparation for further development is going on beneath the gum.
At the end of this period, namely, about the sixth year, the next stage in the production of the adult condition begins. It consists in the eruption of four new teeth-the first permanent molars-one on each side, above and below, behind those of the deciduous set. This is followed by the gradual falling out of the twenty teeth which have occupied the mouth since the second year (Fig. 879), and the substitution for them of twenty new teeth, which take up, one by one, the vacancies created by the dropping out of each of the deciduous set.. Finally, the adult condition is attained by the eruption of eight additional teeth-the 2nd and 3rd molarstwo on each side, above and below, behind those which have already appeared. All of these the permanent teeth-have appeared by the end of the twelfth or thirteenth year, except the four dentes serotini (O.T. wisdom teeth), which are usually