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The oral cavity is the first portion of the entire digestive tract. It is an irregularly shaped, elongated cavity, situated in the lower portion of the face, and its boundaries are partly bony and partly musculocutaneous. It is divided by the two rows of teeth into two incompletely separated spaces, the vestibulum oris and the oral cavity proper.

 


The vestibulum oris.

The vestibulum oris (also termed the buccal cavity) is a narrow, somewhat semicircular space situated between the cheeks and lips and the teeth. When the upper and lower teeth are in apposition it communicates with the oral cavity proper behind the last molar tooth, and it communicates with the outer world through the oral orifice (rima oris).
This is bounded by the lips, which are connected at the angles of the mouth by the labial commissures and form the greater portion of the anterior wall of the vestibule. The upper lip is longer than the lower and its external surface presents a rather broad, shallow, median furrow, known as the philtrum, which runs downward toward the vermilion border and terminates in the tubercle of the upper lip. The upper lip is separated from the cheek by the nasolabial groove, which passes outward and downward in a slight curve from the ala of the nose. The outer surface of the lower lip is traversed by the metUolabial groove, a transverse furrow which separates it from the chin.
The lips are composed of the skin, the labial muscles, and the labial mucous membrane, the last containing the labial glands, which are mucous glands varying in size from that of a lentil to that of a small pea.
The posterior surfaces of the lips are connected with the mucous membrane (gingiva) covering the alveolar processes of the maxillae and mandible by thin folds of mucous membrane known as the frenula of the lips. The frenulum of the upper lipp is always longer and more distinct than that of the lower.
Lateraly from the Ups the cheeks (buccce) form the external boundaries of the vestibulum oris. Like the Ups, they consist of integument (with large hairs in the male), of muscles, and of mucous membrane which in this situation is thin and contains the buccal glands partly embedded in the buccinator muscle or even lying upon its outer surface. In the angle between the buccinator and masseter muscles is situated a marked accumulation of fatty tissue, the buccal jot mass.
The portion of oral mucous membrane w r hich envelops the alveolar processes and passes between the teeth to be attached to the interalveolar septa is of considerable thickness and is known as the gum or gingiva. It is firmly attached to the periosteum by its submucous layer and is distinguished from the remainder of the oral mucous membrane by its firm structure.
The posterior wall of the vestibulum oris is formed by the alveolar processes enveloped by the oral mucous membrane and by the anterior or anterolateral teeth.
The buccal mucous membrane also presents the orifice of the parotid duct.


 

The oral cavity proper

The oral cavity proper is bounded above by the palate, which separates it from the nasal fossae. Its floor is formed chiefly by the tongue, which, when the mouth is closed, practically fills the cavity, only a relatively small space remaining between the dorsum of the tongue and the palate. The anterior and lateral boundaries are formed by the dental arches, while posteriorly the cavity is only partly bounded by the velum palatinum and the palatine arches, since it communicates in this direction with the pharynx through the isthmus of the fauces.
The palate, the roof of the oral cavity, is further divided into the hard and the soft palate. The former accurately corresponds to the relief of the hard palate of the skeleton, and its mucous membrane is thick and firm, like that of the gums, and is intimately connected with the periosteum by strong submucous fasciculi. It contains many mucous palatine glands which are of irregular shape and vary in size from 2 to 5 mm.
In the median line the mucous membrane of the hard palate forms a slightly elevated palatine raphe, the anterior extremity of which terminates in a small, rounded, wartlike projection, the incisive papilla* which corresponds to the position of the incisive foramen. Anteriorly it also presents three or four transverse palatine folds or ruga, the development of which is subject to considerable variation.
The soft palate or velum palatinum is a muscular plate, richly supplied with glands and covered upon both surfaces by mucous membrane, which separates the oral cavity from the nasal portion of the pharynx. It hangs obliquely downward and backward, its base being attached to the posterior border of the bony palate and its anterior surface directly continuous with the mucous membrane of the hard palate. At either side it is continuous with the palatine arches which form the lateral boundaries of the fauces and it terminates below and behind in a round conical appendage, the uvula, whose tip, when its muscles are at rest, is curved forward. The anterior surface of the soft palate is concave and directed toward the oral cavity, the posterior is convex and looks toward the pharynx. The mucous membrane of the soft palate is fairly smooth, although it is thrown into slight folds by the relaxation of the muscles; it is thinner than that of the hard palate and contains a much greater number of mucous palatine glands, which are also larger and more closely crowded together. The lateral portions of the soft palate constitute the two palatine arches, two folds of mucous membrane containing muscles, which form the lateral boundaries of the isthmus of the fauces.
The more anterior fold, the glosso palatine arch, passes in a curve from the lower margin of the soft palate to the mucous membrane of the lateral border of the tongue, where it broadens somewhat and terminates as the plica triangularis. The posterior or pharyngo palatine arch is thicker and straighter than the anterior one and extends between the soft palate and the outer wall of the oral portion of the pharynx.
Between the palatine arches upon either side is found the tonsillar sinus, in which is situated the palatine tonsil, a somewhat flat, oblong elevation upon the surface of which deep fissures or depressions, the fossulae tonsillares, are visible. Its borders are not very sharply circumscribed, but it fills more or less completely the space between the two palatine arches. Just above the tonsil there is frequently a deep triangular pit, the supraton-sillar fossa, which is believed to be the remains of the second pharyngeal pouch of the embryo.
It contains the orifices of mucous glands which are everywhere so plentiful in the tonsillar region.
Both the soft palate arid the palatine arches contain muscles which are termed the palatal and pharyngeal muscles. They are the following:
The azygos uvula (m. uvula) is a small, unpaired, flat, elongated muscle which arises from the posterior nasal spine and terminates in the apex of the uvula, being situated nearer its posterior than its anterior surface. It not infrequently shows indications of being a paired muscle.
The levator veli palatini (petrosal pin gostaphylinus) is a rather flat, elongated, paired muscle which arises from a rough area near the carotid foramen upon the inferior surface of the petrous portion of the temporal bone, and from the lower margin of the posterior extremity of the cartilaginous portion of the tuba auditiva. It passes downward and inward in the outer wall of the nasal portion of the pharynx to the soft palate, where it spreads out in a flat lamina, the fibers of which interlace with those of the opposite muscle and with the pharyngopalatinus and azygos uvulae, forming with these muscles an almost continuous muscular plate, situated nearer the posterior than the anterior surface of the soft palate, being separated from the latter surface by a thick mass of glands.
The tensor veli palatini (sphenosalpingostaphylinus) is a thin, flat, elongated muscle which arises by a short tendon from the spine of the sphenoid, from the scaphoid fossa of the internal pterygoid process, and from the outer wall of the cartilaginous tuba auditiva. It is intimately related with the internal surface of the pterygoideus internus, from which it is separated only by the buccopharyngeal fascia. The levator veli palatini is more internal and further posterior than the tensor veli palatini, from which it is separated by fatty tissue.
Above the hamular process of the internal pterygoid plate the posterior surface of the muscle passes into a narrow tendon which winds around the hamular process in the sulcus hamuli and broadens out into an aponeurosis which passes almost horizontally across the soft palate to join its fellow of the opposite side. A small bursa, the bursa m. tensoris veli palatini, separates the tendon from the bone. The aponeurosis formed by the tendons of the two tensores veli palatini is attached to the posterior margin of the bony palate and is situated in front of the radiating fibers of the levatores.
The glossopalaiinus is a flat muscular bundle which forms the anterior palatine arch. It arises from the transverse fibers of the tongue and inserts into its fellow of the opposite side in the base of the uvula, being also connected with the radiations of the levator veli palatini.
The pharyngopalatinus is better developed than the preceding muscle and forms the posterior palatine arch. It has manifold connections with the constrictors of the pharynx and may consequently be regarded as one of the pharyngeal muscles.
A portion of it comes directly from the constrictor medius and the remainder takes origin from the posterior margin of the thyreoid cartilage in connection with the inferior constrictor. In the soft palate the muscle has relations similar to those of the glossopalatinus and is particularly intimately connected with the radiation of the levator veli palatini.
The tensor veli palatini is innervated from the third division of the trigeminus through the otic ganglion; the remaining muscles are supplied from the pharyngeal plexus by fibers from the spinal accessory and pneumogastric nerves. The levator veli palatini and pharyngopalatini constrict the isthmus of the fauces.
The oral mucous membrane varies in character and thickness in different localities. In the floor of the mouth, in the sublingual region, it is thin and is separated from the underlying tissue by a loose submucous layer. In the gums and hard palate it is especially thick, and the sub-mucous layer in these situations is firmer and immovably connects the membrane with the peri- osteum. It is also thick upon the dorsum of the tongue, beneath which the submucosa becomes the lingual fascia.
A considerable portion of the oral cavity is developed from the so-called oral invagination, an ectodermal invagination which is at first separated from the endodermal intestinal tube by the pharyngeal membrane. At a certain period of development the oral invagination represents both the future oral and nasal cavities, but after the disappearance of the pharyngeal membrane and the union of the invagination with the anterior portion of the primitive gut, the oral and nasal cavities are separated by the paired palatal plates which develop from the superior maxillary processes and fuse in the median line. The lips are formed anteriorly during the formation of the face from the maxillary and mandibular processes of the first visceral arch.


 

The teeth

The teeth are hard conical structures, whose roots are embedded in the alveoli of the jaws. The portion of the tooth surrounded by the gums is called the neck (collum dentis), while the portion projecting into the oral cavity is designated as the crown (corona dentis).
The three chief constituents of a tooth are the enamel (substantia adarnantina), the dentine (sub- stantia eburnea), and the cement (substantia ossea). The enamel is found only in the crown, while the cement is present chiefly about the root, although it forms a very thin layer about the neck of the tooth, where the enamel and the dentine become thinner. The enamel has a white glistening surface with a bluish or yellowish shimmer, while the root of the tooth is slightly yellowish and dull.
In the crown of each tooth there may be recognized a masticatory surface directed toward its fellow in the opposite jaw, a labial or buccal surface directed toward the lip or the cheek respectively, a lingual surface in relation with the tongue, and two contact surfaces in apposition with the neighboring teeth.
The root of the tooth is single or multiple and is generally conically shaped. At its apex is a foramen, the external orifice of the canal of the root, which extends throughout the length of the root, and in the region of the neck gradually dilates to a large cavity situated within the crown, the tooth cavity, also known as the pulp-cavity because it is filled by a soft non-calcified tissue, the dental pulp. The shape of the pulp-cavity is in general a reproduction of that of the entire tooth, but it not infrequently presents fine irregular ramifications.
The entire set of teeth, thirty-two in number in the adult, is known as the denture, and is arranged in an upper and a lower row, the superior and the inferior dental arch. The upper row is fixed in the alveoli of the superior maxilla and the lower row in those of the mandible, the form of articulation being that known as gomphosis. The bone and the tooth are separated by a thin layer of tissue common to both structures, the alveolar periosteum, which in the vicinity of the neck of the tooth is also designated the circular ligament. The teeth of the two rows resemble each other in shape and size, although the similarity is not absolute, and the number of teeth in each row is the same, namely, sixteen.
The teeth of each jaw are divided into four different groups according to their shape, the incisors, the canines, the premolars, and the molars, and each of the four varieties possesses such well-defined characteristics that transitional types do not occur, although differences are observed between individual teeth of the same group, particularly between those of the upper and lower jaw.
In each jaw there are four incisors, two canines, four premolars and six molars, the arrangement of the individual groups being the same in both jaws. The incisors are placed most anteriorly, the two central ones being in contact in the median line; then come on either side a canine, two premolars, and three molars, these last being situated most posteriorly.
The incisor teeth have flat, chisel-shaped crowns, convex on the labial surface and concave on the lingual surface, and thicker but narrower at the base and broader and thinner at their free margins. Upon the labial surface are three longitudinal ridges which are not always distinctly marked, and upon the cutting-edge of a recently erupted tooth these ridges terminate as small projections which rapidly disappear as a result of attrition. The inner corners of the cutting-edge are usually sharper than the outer ones, these being generally rounded off.
The crowns of the incisors lie in the frontal plane and present an inner and an outer surface of contact. The roots are rounded, of average length, and usually exactly straight; those of the lateral incisors are somewhat shorter and slightly flattened.
The upper incisors are always larger than the lower, and the upper central incisor is always larger than the lateral, but in the lower jaw this relationship is reversed. The relative size of the incisor teeth is subject to marked individual variations.
The canine teeth are situated between the incisors and the premolars and are of an elongated conical form. Their large, thick, irregularly conical crowns are approximately in the frontal plane, so that they present a labial and a lingual surface, and an inner and an outer surface of contact. The labial surface is markedly convex, and the lingual is characterized by a slight elevation. The roots are very long and conical, although they are distinctly flattened, particularly in the lower jaw. In consequence of their long roots the canines are the longest teeth of the entire dentition, and, moreover, their crowns are higher than those of the other teeth. The cusp of the crown is blunt and not exactly in the middle of the tooth, but some-what nearer its inner side.
The premolars are characterized by bicuspid crowns which are flattened from before backward, and consequently present an anterior and a posterior contact surface, a convex lingual surface, and a larger convex buccal surface. The cusps or tubercles are separated by an almost sagittal groove in such a manner that the lingual cusp is smaller than the buccal one; indeed, the lingual cusp of the lower first premolar is usually poorly developed, but that of the lower second premolar is usually double, so that this tooth, which is usually the largest of the premolars, is frequently tricuspid.
The roots of the lower premolars are always single, of medium length, and distinctly flattened.
Those of the upper premolars vary considerably; that of the first is usually double or at least bifid, while that of the second is generally markedly flattened or furrowed and usually possesses a double root canal.
All the molars possess a number of cusps and roots, and their crowns are low and characterized by their large circumference. The number of the roots and the position of the cusps are different in the upper and lower jaw, the upper molars being usually somewhat smaller than the lower and having three roots, while the lower ones have but two. The first molar in each jaw has the largest and highest crown, while the third has the smallest and the lowest, and, consequently, as a rule; the first lower molar is the largest of the group.
The cusps of the molar teeth are four, rarely five in number, two being lingual and two buccal. In the lower molars the four cusps are separated by a tolerably regular cruciform groove, and since the Ungual cusps are higher than the buccal ones, the lower molars look as though they were composed of two fused premolars. The lower first molar usually has five cusps, three buccal and two lingual. In the upper molars the buccal cusps are higher than the lingual and the separating sulci have the form of a slanting H, so that the lingual and buccal cusps hold an oblique relation to each other. Irregularities in the number and arrangement of the cusps are common, particularly in the third molar (wisdom tooth, see below), which may have from three to five cusps. As in the case of the premolars, the frontal surfaces of the crowns of the molars are in relation with each other, so that an anterior and a posterior surface of contact may be recognized. Both the lingual and the buccal surfaces of the molar crowns are convex, and both surfaces of the upper molars (at least of the first) have a longitudinal sulcus, while in the lower molars only the buccal surface presents this marking.
The lower molars have two roots, an anterior and a posterior, which are sometimes grooved.
They are of moderate length, compressed in the frontal plane, and their apices are usually bent backward. The grooves are an indication that each root is formed by the fusion of two halves, and in rare instances more than two roots may consequently be present.
The upper molars have three conical roots the ends of which are also bent backward. Two are buccal and one is lingual (or palatine, i. e. } directed toward the palate, posterior). All three roots are well developed in almost all cases in the first upper molar, while they may be more or less fused in the second. The latter condition is the rule in the third.
The third molars do not make their appearance until from the twentieth to the twenty-fifth year, and have consequently been called the "wisdom teeth" {denies serotini). They are only rudimentary structures in civilized nations, but in ancient skulls and in those of many savage races they are well developed and frequently but slightly smaller than the second molars. The upper wisdom tooth is always much smaller than the lower, and its roots are usually fused together, although the original number is frequently indicated, particularly by the number of the root-canals. There are frequently only three cusps present. The lower wisdom tooth usually has two short roots and the crown seems better developed than that of the upper jaw.
The upper teeth, particularly the front ones, are normally directed slightly outward; those of the lower row slightly inward, so that the somewhat larger superior dental arch overlaps the smaller inferior one throughout its entire circumference. When the dental arches are in apposition (the so-called position of articulation of the teeth) every tooth is opposed to two teeth of the other jaw, except in the cases of the upper third molars, which are in contact only with the lower third molars; this condition is due to the front teeth of the upper row being considerably wider than those of the lower.
In contrast to the thirty-two permanent teeth forming the adult dentition is the deciduous or "milk" dentition of childhood, which contains but twenty deciduous teeth, namely, eight incisors, four canines, and four molars.
The deciduous incisor and canine teeth, although smaller, correspond to those of the permanent denture not only in number but likewise in peculiarities of shape. They are also found in the same situation as the permanent teeth of the same name, while the deciduous molars appear at the site of the subsequent premolars. They resemble the permanent molars in having several roots, and in being provided with several cusps. The second (posterior) milk-molars are always larger than the first. The upper molars, like those of the permanent dentition, have three roots, two buccal and one lingual, but these roots present a marked tendency toward fusion. The lower molars have two roots, and the crowns of both the upper and lower teeth have from four to five irregularly situated cusps.
The teeth of the lower jaw erupt normally before those of the upper.
The lower central incisor makes its appearance usually in the sixth or seventh month and is soon followed by the corresponding tooth in the upper jaw (in the seventh to the eighth month). The lateral incisors usually erupt in the eighth to the twelfth month, and the lower first molars in the twelfth to the sixteenth month, followed several months later by those of the upper jaw. After the first molars come the canines (sixteenth to twentieth month) and finally the second molars (twentieth to thirtieth month).
The milk-teeth are gradually replaced by the permanent dentition, so that during a certain period in childhood teeth of both sets may be seen alongside of each other, and at this stage the jaws consequently contain a large number of teeth in different stages of development. The first permanent tooth to erupt is the lower first molar, which makes its appearance from the fifth to the eighth year and is speedily followed by the corresponding tooth in the upper jaw. The deciduous central incisors are not replaced until the sixth to the ninth year, and the lateral from the seventh to the tenth year. The first premolars erupt from the ninth to the thirteenth year, the permanent canines from the ninth to the fourteenth year, and the second (posterior) premolars from the tenth to the fourteenth year, these last being almost immediately followed by the second molars. The third molars frequently do not make their appearance until quite late (the sixteenth to the fortieth year). The upper premolars usually erupt before the lower, but with this exception the teeth of the lower jaw always appear first.
The crown of the tooth is formed first and the so-called enamel-organ takes part in its formation only, since it alone possesses enamel. The roots are formed by the dental papillae and are not complete when the eruption of the tooth occurs and the cement and the circular ligament are formed by the wall of the dental sac. During the development of the tooth the pulp-cavity and particularly the root-canals are relatively large.
The roots of the deciduous teeth are eventually absorbed by the action of osteoclasts, and their crowns either fall out or are broken off mechanically.
Dental anomalies are not common, although supernumerary teeth may be observed and normal teeth may be wanting. The upper lateral incisors are most frequently absent, in which case the central incisors are correspondingly enlarged, and supernumerary teeth most frequently occur in the incisor set. Anomalies of position are common. Very rarely there is observed the beginning of a third dentition.


 

The tongue (Lingua)

The tongue is a muscular organ which almost entirely fills the oral cavity. It is covered with mucous membrane and consists of three chief portions: the middle and largest portion, attached to the floor of the mouth, the body; the anterior portion, projecting into the oral cavity, and completely clothed by mucous membrane, the tip; and the posterior portion, attached to the hyoid bone and epiglottis, the root.
In the body of the tongue there may be recognized an inferior attached surface and a convex superior surface or dorsum which is covered throughout its entire length by the oral mucous membrane. The lateral margin of the tongue is rounded; in its anterior part it is free, while posteriorly it is continuous with the soft palate.
When the mouth is closed, the larger anterior portion of the dorsum of the tongue is applied to the palate; its posterior portion borders upon the pharynx at the isthmus of the fauces. The junction of the body with the root of the tongue is indicated upon the dorsum by a depression, the joramen ccecum, which leads into a short blind mucous canal, the lingual duct, an embryonic rudiment which in the adult exhibits only the orifices of a few mucous glands. From the foramen caecum the circumvallate papillae (see below) extend laterally, being arranged like a letter V, the apex of which is directed posteriorly and is formed of the foramen caecum itself. Parallel and just posterior to the circumvallate papillae there is frequently a groove, the sulcus terminalis, which indicates the dividing-line between the body and the root of the tongue.
If this be absent, the row of circumvallate papillae forms the boundary.
The root of the tongue is connected with the epiglottis by three folds of mucous membrane, a single median glosso-epiglottic fold and two lateral glosso-epiglottic folds. Between these folds upon either side of the median line there is a roundish pit which is known as the epiglottic vallecula.
In the tongue two chief constituents, the mucous membrane and the musculature, may be recognized. Upon the under surface of the tongue these two constituents are but loosely attached to one another, but upon the dorsum the attachment is firmer, the terminal prolongations of the muscle fibers inserting directly into the lingual fascia, a layer of firm connective tissue situated immediately beneath the mucous membrane.
Upon the dorsum of the tongue the mucous membrane is sharply divided by the sulcus terminalis or the circumvallate papillae into a portion covering the body and a portion covering the root of the organ, and the two portions differ from each other in such a way that the anterior one may be termed the papillary portion and the posterior the tonsillar.
The anterior portion owes its characteristic velvety appearance to the lingual papillae, which are in general of a conical shape and project above the level of the mucous membrane.
According to their shape, the following varieties may be recognized :
1. The filiform papilla have the form of elongated cones rather than of cylinders, and are present in large numbers over the entire papillary portion of the mucous membrane, and especially at the sides and tip of the tongue, where they attain their greatest length. The great majority of the lingual papillae are of this type.
2. The conical papillce are found scattered among the filiform structures and are not sharply differentiated from them.
3. The fungiform papillce occur scattered among the filiform papillae at the sides and tip of the tongue and are characterized by having the top broader than the base or pedicle. A sub-variety of these constitute:
4. The lenticular papillce, which are low T er than the fungiform but otherwise similar to them.
5. The circumvallate papillce (papillae vallatae), so named because they are surrounded by a circular wall-like elevation of the mucous membrane. They resemble the fungiform in shape, but are larger, and their surfaces are frequently slightly depressed beneath the general surface. In their more minute structure, however, they differ markedly from the fungiform papillae.
They are few in number and are always arranged in a typical manner upon the dorsum of the tongue. Their number varies between seven and twelve, and they are arranged in a V- shaped manner, the apex (of the V) being at the foramen caecum. They may be situated at unequal distances from one another and rarely they are arranged in two rows.
6. The foliate papillce are but rudimentary structures in the human subject. They are arranged in several parallel transverse folds, usually only faintly indicated, upon the lateral margins of the tongue just in front of the glossopalatine arch. Unlike the other transverse folds and wrinkles in the relaxed tongue of the dead subject, the folds or laminae of the foliate papillae are not obliterated by traction.
(For further details concerning the structure of the lingual papillae see the Sobotta-Huber "Atlas and Epitome of Normal Histology," Saunders' Medical Hand-Atlases.)
The posterior tonsillar portion of the lingual mucous membrane is markedly different from the anterior papillary portion. It is characterized by the presence of lymphatic structures, the lingual follicles, which together form a diffuse tonsillar structure, the lingual tonsil, and it is also particularly rich in mucous glands. Each lingual follicle forms a small rounded elevation with a fine central opening; at the root of the tongue they form a dense compact mass, while toward the epiglottis and the adjacent palatine tonsil they are more scattered.
The sublingual mucous membrane is smooth and thin and exhibits the ordinary characteristics of the oral mucous membrane. In the median line, beneath the tip of the tongue, it presents a fold, the frenulum, to either side of which is found a plica fimbriaia, which is always well developed in the newborn and less distinct, though rarely entirely absent, in adult life. This fold is always lobulated in the newborn, and usually so in the adult, and gradually disappears as it runs backward and outward from the anterior extremity of the frenulum. In the floor of the mouth just beside the anterior portion of the lateral margin of the tongue, and running obliquely from behind forward and inward, is a fold, the sublingual fold, which is produced by the underlying secretory duct of the sub-maxillary gland and usually contains the orifices of the lesser sublingual ducts. The two folds converge toward the posterior extremity of the frenulum, in the immediate proximity of which they terminate in a small elevation, the sublingual caruncle, which marks the orifice of the submaxillary duct.


 

The lingual muscles

The muscles of the tongue are divided into two groups: (1) Those which take origin from the skeleton (skull and hyoid bone) and insert into the tongue; (2) those muscles which belong solely to the tongue, both the origin and insertion being situated within the organ. The first group is composed of the genioglossus, the hyoglossus (chondroglossus), and the styloglossus.
The genioglossus is the strongest of all the lingual muscles and arises by a tendon from the mental spine (superior genial tubercle) of the mandible. It is a paired muscle and is situated just to one side of the median line so that the internal surfaces of the two muscles are in opposition. The majority of the fibers terminate in the lingual mucous membrane, or rather in the lingual fascia, but the most inferior fasciculi pass almost horizontally backward immediately above the geniohyoid and insert into the body of the hyoid bone and into the epiglottis (by means of elastic tendinous fasciculi). The adjacent fibers also at first pass backward from their point of origin, but soon curve sharply upward to insert into the mucous membrane of the dorsum, while the most anterior fibers pass almost vertically upward and then curve slightly forward into the tip of the tongue.
The hyoglossus is a flat quadrangular muscle situated at the side of the floor of the mouth, and arises from the body and greater and lesser cornua of the hyoid bone. The portion coming from the lesser cornu, which is known as the chondroglossus, is not always present. The portion of the muscle arising from the body of the hyoid bone is the strongest, that originating from the greater cornu being considerably flatter, and the fasciculi from both origins pass obliquely upward and forward into the tongue, where they pass between the longitudinalis inferior and the styloglossus, partly interlacing with the latter muscle. The fibers of the chondroglossus, concealed by the remaining portions of the hyoglossus, pass from the lesser cornu to the dorsum of the tongue to mix with the fibers of the longitudinalis superior.
The styloglossu is a well-defined muscle which arises from the styloid process of the temporal bone and frequently also from the stylohyoid and stylomandibular ligaments. It becomes markedly flattened as it approaches the tongue and is inserted principally into the lateral margin of that organ as far forward as the tip, lying laterally to the hyoglossus and longitudinalis inferior, some of its fibers also being continuous with the muscular layer designated as the longitudinalis superior. Smaller fasciculi, situated internally and above, penetrate obliquely into the posterior portion of the tongue as far as the median line.
The muscles situated entirely within the tongue are as follows:
1. The longitudinalis inferior, a flat well-defined muscle upon the lower surface of the tongue, situated between the genioglossus and hyoglossus behind and between the styloglossus and genioglossus in front. Its fibers run in the sagittal plane.
2. The longitudinalis superior, a layer of sagittal muscular fasciculi placed immediately beneath the mucous membrane of the dorsum of the tongue and largely made up of prolongations from the other lingual muscles. It is consequently not a separate and distinct muscle.
3. The transversus linguae, composed of a large number of muscular fasciculi which run almost transversely from the median septum to the surface of the lingual mucous membrane, in such a manner that they are intersected by numerous vertical and sagittal fasciculi, and finally insert between the lamellae of the radiating fibers of the genioglossus. The fasciculi of the glossopalatinus are intimately connected with the transversus linguae and some of them originate from it.
4. The verticalis (perpendicular is) linguae includes all the fasciculi which pass vertically through the tongue from the dorsum to the sublingual mucous membrane.
Between the two genioglossi in the median plane there is a connective-tissue partition usually containing fat, the septum, which fades away as it approaches the dorsum and does not reach the mucous membrane. It gives origin to the fasciculi of the transversus.
The fibers of all the lingual muscles interlace abundantly, especially toward their insertions, which are not actually into the mucous membrane proper but rather into the adherent lingual fascia.
All the lingual muscles are supplied by the hypoglossal nerve.
The development of the tongue is intimately connected with that of the oral cavity. The portions of the tongue situated in front of and behind the sulcus terminalis are formed independently, the anterior portion arising partly from the paired mandibular processes and partly from the so-called tuberculum impar which forms the middle of the anterior portion of the tongue, while the root originates from portions of the second and third visceral arches.


 

The glands of the oral cavity (the salivary glands)

The glands which secrete the saliva are divided into two groups: the numerous small glands in the walls of the oral cavity and the three large (paired) salivary glands.
The latter are the parotid, the submaxillary, and the sublingual. They possess excretory ducts of varying lengths, which empty into the oral cavity.
The parotid, the largest oral salivary gland, is of a flattened irregular triangular shape and is situated in front of the external ear in the parotideo-masseteric region and partly also in the retromandibular fossa. Its slightly convex external surface is covered by the skin, the prolongations of the platysma (and risorius), and the parotideo-masseteric fascia, while the slightly concave internal surface rests chiefly upon the masseter.
The anterior portion of the gland is much the thinner, and the anterior somewhat concave margin is slightly beveled and lies upon the external surface of the masseter. The inferior margin is directed somewhat posteriorly, so that it forms an acute angle with the anterior margin, this tip of the gland being situated in the neck and sometimes extending as far down as the sub-maxillary gland. The inferior and posterior margin rests upon the anterior margin of the sternocleidomastoid and the superior margin is generally irregular and is in relation with the zygoma and the external auditory meatus.
The posterior portion of the gland, situated behind the posterior margin of the masseter, covers the outer surface of the ramus of the lower jaw, and its retromandibular process extends behind the ramus to come into relation with the internal pterygoid, the posterior belly of the digastric, and the muscles coming from the styloid process. This glandular process usually also reaches as far as the internal carotid artery and the internal jugular vein.
The parotid gland is traversed by the branches of the facial nerve which are situated nearer the internal than the external surface and form the parotid plexus within its substance. The upper branches of the external carotid, particularly the superficial temporal and some of its ramifications, as well as the posterior facial (temporo-maxillary) vein, may also be more or less enveloped by the lobules of the gland.
The duct of the parotid gland, the parotid duct (ductus Stenoni), appears at the upper portion of the anterior margin of the gland and passes almost transversely across the masseter, bends just in front of its anterior margin, and passes through the fatty tissue in this situation (the buccal fat pad) and the buccinator to the buccal mucous membrane which it perforates obliquely. The orifice of the duct is in the vestibulum oris and appears as a rounded slit opposite the upper second molar tooth.
Several small conglomerations of lobules are very frequently observed about the parotid duct and are known as the accessory parotid gland. The parotid gland is grayish-yellow or yellowish-brown in color and seems distinctly lobulated like the other salivary glands, but the lobules are quite small; at the margins of the gland they are frequently isolated, but throughout the chief mass of the structure they are arranged compactly.
The submaxillary gland is a rounded structure, the long axis of which is in the sagittal plane. It is found in the neck, in the submaxillary region, immediately beneath the platysma and the cervical fascia, the latter structure forming a fibrous capsule for the gland.
The greater portion of the submaxillary gland lies beneath the mylohyoid muscle in the space between the angle of the jaw and the two bellies of the digastric. It also borders upon the stylohyoid and styloglossus, and its internal surface is in relation with the hyoglossus.
The external maxillary (facial) artery and its accompanying vein run in the immediate vicinity.
The upper margin of the gland rests against the body of the jaw and is lodged in a depression which is not always distinct, the submaxillary depression.
The gland is yellowish-white in color and is distinctly lobulated, the lobules being considerably larger than those of the parotid. A thin and markedly flattened glandular process extends upward between the internal pterygoid and the mylohyoid to the sublingual gland and accompanies the secretory duct for some distance.
The submaxillary duct (ductus Whartoni) is the size of an ordinary quill; it is given off from the upper part of the gland and runs above the mylohyoid, between that muscle and the mucous membrane of the floor of the mouth (or the sublingual gland), passing from behind forward and inward and producing the sublingual fold. The orifice in the oral cavity is situated on the sublingual caruncle beside the frenulum beneath the tip of the tongue
The sublingual gland is an elongated flattened structure with its long axis in the sagittal plane, and may be distinctly seen beneath the mucous membrane of the floor of the mouth when the tip of the tongue is raised. The external border is lodged in a depression in the inferior maxillary bone, the sublingual depression, and the posterior margin is in relation with the submaxillary gland, the internal margin with the genioglossus, and its lower surface rests upon the mylohyoid. In the immediate vicinity of the gland are the sublingual artery and the lingual nerve.
The gland is white or light-gray in color and has distinct lobules which are smaller than those of the submaxillary. It is the smallest of the three salivary glands and is not so compactly arranged, frequently consisting of several glandular masses which are only loosely connected.
It does not possess a common duct, but the secretion from the distinctly separated glandular components is poured out through ten or twelve ducts known as the lesser sublingual ducts (ducts of Rivinus), which empty immediately into the oral cavity by a number of small punctiform orifices in the region of the sublingual fold. The anterior portion of the gland, however, frequently gives off a somewhat larger duct, which is known as the greater sublingual duct (duct of Bartholin), and this either empties independently at the sublingual caruncle beside the submaxillary duct or pours its secretion into the latter structure immediately before its termination. Both the submaxillary and the sublingual glands consequently empty into the oral cavity, while the orifice of the duct of the parotid gland is situated in the vestibulum oris.
The tube there is an inconstant elevation caused by the underlying levator veli palatini, and a rather distinct fold, the salpingopharyngeal fold, extends from the torus tubarius to the lateral pharyngeal wall, where it gradually disappears, and above and behind the torus tubarius the pharyngeal fornix upon either side forms a narrow blind pocket, the pharyngeal recess (cavity of Rosenmuller). Between the two tubal orifices and actually in the roof of the pharynx is situated the pharyngeal tonsil, a lymphatic structure which is usually distinct only in children.
The oral portion of the pharynx communicates with the oral cavity through the isthmus of the fauces, the boundary being marked by the pharyngopalatine arches. It is the narrowest portion of the pharynx and presents no special structures, except a fold of mucous membrane, the pharyngo- epiglottic fold, which passes from the lateral margin of the epiglottis to the outer pharyngeal wall and separates the oropharynx from the laryngopharynx.
The laryngeal portion of the pharynx is the only portion which has an extensive anterior wall. It lies behind the larynx, the posterior wall of which is distinctly visible through the thin pharyngeal mucous membrane, so that there may be recognized a median elevation produced by the plate of the cricoid cartilage (and the arytenoid cartilages) and two deep lateral depressions which correspond to those between the cricoid and arytenoid cartilages internally, and the posterior surface of the thyreoid cartilage externally. These lateral depressions are termed the piriform recesses and present a fold of mucous membrane, the fold for the laryngeal nerve, which passes obliquely from above downward and from without inward, and contains the superior laryngeal nerve. In the laryngopharynx is also situated the entrance to the larynx or aditus laryngis.
The pharyngeal wall consists of a mucous membrane, of a submucous layer, and of a muscular coat. The mucous membrane is red and smooth, rather thin in its inferior portion, and contains small mucous pharyngeal glands, especially abundant in the upper portion.
In this upper portion the musculature is absent for a distance of about two centimeters, and the submucosa in this situation forms a strong fibrous membrane which is designated as the pharyngobasilar fascia (pharyngeal aponeurosis) and inserts into the base of the skull.
The muscular coat of the pharynx is found in the lateral and posterior walls with the exception of the uppermost pftrtion. It consists practically of circular fibers which meet in the median line, the pharyngeal raphe, and partly interlace, and in it there may be recognized three flat, thin muscles situated one above the other and known as the constrictors of the pharynx.
The constrictor pharyngis superior (cephalo pharyngeus) is composed of four portions, named according to their origins, which unite to form a single muscular lamina in the lateral wall of the pharynx. The uppermost fasciculi coming from the hamular process and the contiguous portion of the internal plate of the pterygoid process are designated as the pterygopharyngeus; the next fasciculi are those of the buccopharyngeus and represent the backward continuation of the buccinator, from which ihey: are separated by TFe pterygomandibular raphe; the mylo pharyngeus comes from the posterior part of the mylohyoid line of the mandible; and the small glossopharyngeus, the most inferior portion, originates in the lingual musculature, chiefly from the fasciculi of the transversus linguae.
The constrictor pharyngeus medius (hyo pharyngeus) arises from the lesser (chondro pharyngeus) and the greater (cerato pharyngeus) cornua of the hyoid bone. Only the middle fasciculi pass horizontally to meet in the median raphe, both the upper and the lower fasciculi running obliquely (upward or downward as the case may be) and consequently meeting in the raphe at an acute angle. As a result of this insertion the upper apex of the muscle covers the constrictor pharyngis superior, while the greater portion of the muscle is itself covered by the constrictor pharyngis inferior.
The constrictor pharyngis inferior (laryngo pharyngeus) is the largest and much the longest of the pharyngeal constrictors. It consists of two portions which are separated only at their origins. The larger superior portion, known as the thyreo pharyngeus, arises from the entire outer surface of the plate of the thyreoid cartilage, extending from the superior to the inferior cornu; the smaller inferior portion, termed the crico pharyngeus, comes from the outer surface of the ring of the cricoid cartilage. The fibers of this latter portion run almost horizontally; the fibers of the upper portion, on the contrary, pass obliquely upward (the uppermost ones rather sharply) and form an acute angle, the apex of which is directed upward and conceals the greater portion of the constrictor medius.
The stylo pharyngeus acts as an elevator of the pharynx. It arises from the inner side of the styloid process of the temporal bone at the side of and behind the pharynx, and forms a slender, slightly flattened muscle which broadens as it approaches its insertion. The majority of the fibers pass into the lateral wall of the pharynx between the superior and inferior constrictors, with which they interlace, especially with the latter. A few fasciculi also pass to the lateral margin of the epiglottis and to the upper margin of the thyreoid cartilage.
The diaphragm and the pylorus of the stomach are drawn upward and the stomach is rather strongly contracted.
The salpingo pharyngeus is an inconstant muscle situated in the fold of the same name, which arises from the cartilaginous end of the tuba auditiva (Eustachian tube) and passes to the lateral wall of the pharynx.
The pharyngeal muscles are innervated through the pharyngeal plexus (see Neurology).

Human Anatomy (1909) by DR. Johannes Sobotta (1869-1945) Professor of Anatomy in the university of Wurzburg

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