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From the posterior surface of the glosso-palatine arch a thin triangular fold of mucous membrane, called the plica triangularis, passes backwards. Its base corresponds to the glosso-palatine arch, its superior border is free, and passes downwards and backwards, frequently overlapping the tonsil. Its lower border is attached to the side of the tongue. It covers, medially, the inferior part of the tonsillar fossa. The palatine tonsil presents very different forms in different individuals.
It may project from the fossa into the cavity of the pharynx, or it may be flat and limited to the tonsillar fossa. In some cases the plica triangularis is fused with the free surface of the tonsil, and the lymph tissue may in some cases be developed on the medial surface of that plica.
FIG. 905.-HORIZONTAL SECTION THROUGH MOUTH AND PHARYNX AT THE LEVEL OF THE PALATINE TONSILS. The stylopharyngeus, which is shown immediately to the medial side of the external carotid artery, and the prevertebral muscles, are not indicated by reference lines.
The palatine tonsils are oval in shape, with the long axes directed vertically, and each presents a medial and a lateral surface, and a superior and inferior pole, and an anterior and posterior margin.
The medial surface is prominent and free, studded with small pit-like depressions called the fossulæ or crypts of the tonsil.
The lateral, or attached surface, is enclosed in a distinct fibrous capsule, connected with the pharyngo-basilar fascia, and this capsule separates the tonsil from the superior constrictor muscle of the pharynx.
The superior pole is rounded and blunt, and presents numerous fossulæ. The inferior pole projects downwards towards the tongue. The anterior margin looks towards the glosso-palatine arch, and is often overlapped by the plica triangularis, the posterior margin is directed towards the pharyngo-palatine arch.
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Relations of the Tonsil.-The lateral relations of the tonsil consist of the fibrous capsule and the superior constrictor muscle. Lateral to the pharyngeal wall lies the internal pterygoid muscle, and behind it a region filled with connective tissue, containing blood-vessels and nerves.
The nearest and most important vessel is the external maxillary artery, which, especially if tortuous, has a very close relation to the pharyngeal wall at this level.
The ascending palatine and tonsillar branches of the artery are also in close relation.
The internal carotid artery and internal jugular vein lie considerably further back ( to 1 inch) and to the lateral side, and the external carotid artery is still more lateral.
The ascending pharyngeal artery is well behind the tonsil.
The size of the palatine tonsils is extremely variable, but as a rule, in early life, they measure something under 1 inch (20 to 22 mm.) from above downwards, about inch (18 to 20 mm.) antero-posteriorly, and inch (12 to 15 mm.) mediolaterally.
The arteries of the palatine tonsil are derived from the ascending palatine and tonsillar branches of the external maxillary artery, the ascending pharyngeal branch of the external carotid, and the dorsalis linguæ of the lingual. The veins pass to the tonsillar plexus, on the lateral side of the tonsil, which is an offshoot of the pharyngeal venous plexus.
Nerves. The palatine tonsil receives a special branch from the glosso-pharyngeal; this unites with branches from the pharyngeal plexus to form a small plexus tonsillaris which supplies the
The lymph vessels are extremely numerous. They begin in a plexus which surrounds each follicle, whence vessels pass to the lateral surface of the tonsil. Thence they pass through the wall of the pharynx, and pass to the deep cervical glands in the neighbourhood of the greater cornu of the hyoid bone, behind and inferior to the angle of the mandible.
Structure of the Palatine Tonsils.--Each palatine tonsil is composed of masses of small rounded lymph cells with a delicate connective tissue reticulum. These resemble in structure the folliculi linguales, q.v.
Upon its medial surface it is covered with epithelium, continuous with the epithelium covering the adjacent parts of the wall of the pharynx. This surface is very irregular, and on section crypts, termed fossulae tonsillares, are seen to be formed by deep infoldings of the epithelial wall. On its lateral surface, the lymph tissue is invested by a connective tissue capsule.
Pars Laryngea. The laryngeal part of the pharyngeal cavity lies posterior to the larynx (Fig. 903). It is wide above, where it is continuous with the oral portion, and maintains a considerable width until within about an inch of its termination, where, posterior to the cricoid cartilage it narrows rapidly and passes down to join the oesophagus. Except during the passage of food, the anterior and posterior walls of this latter part are in contact, and its cavity is reduced to a mere transverse slit (Fig. 906).
The anterior wall of the laryngeal portion of the pharynx is formed in its whole extent by the posterior surface of the larynx, of which the following parts are seen from the pharyngeal cavity (Fig. 901):-The epiglottis above; below this the superior aperture of the larynx, bounded at the sides by the ary-epiglottic folds; lateral to these folds is seen, on each side, a deep recess, the recessus piriformis (Fig. 905). Lower down still, the muscles and mucous membrane which cover the posterior surfaces of the arytenoid and cricoid cartilages are distinguishable.
Its posterior wall and side walls are directly continuous with the corresponding walls of the oral portion, and present no features which require special notice.
The recessus piriformis (O.T. sinus pyriformis) is a deep depression, seen on each side between the ary-epiglottic fold and the lamina of the thyreoid cartilage. When viewed from above, as in laryngoscopic examinations, it appears of a piriform shape, the wider end being directed upwards and forwards. When viewed from behind, the recess is boat-shaped and elongated in the vertical direction. Its side wall is formed by the thyreoid cartilage and thyreo-hyoid membrane, covered with mucous membrane; its medial wall is formed by the ary-epiglottic fold, and slightly, below, by the superior part of the cricoid cartilage.
Relations of the Pharynx.-In considering the relations of the pharynx, it is at once evident that these are very different in the superior and inferior portions.
1. Throughout its whole extent it lies anterior to the cervical region of the vertebral column, and is separated from the bodies of the vertebræ and the intervertebral fibro-cartilages by the loose areolar tissue of the prevertebral or retropharyngeal space, posterior to which lie the anterior longitudinal ligament of the vertebral column, and the longus capitis and longus colli muscles.
2. In the neck, on each side, it is in contact with the superior part of the thyreoidable gland, the carotid sheath, and especially the common and external carotid arteries, and, more posteriorly, the internal carotids.
The branches arising from the inferior part of the external carotid are also in close relation to the pharyngeal wall, viz., the superior thyreoid and lingual arteries in the lower part, while the external maxillary artery, as it passes under the digastric and stylo-hyoid muscles, comes into contact with the superior constrictor; and the ascending pharyngeal artery runs upwards by the side of the pharyngeal wall. 3. The relations of the cranial portion are more complex, but are of great importance. Reference to Fig. 906 will help to elucidate them. At the upper
FIG. 906.-HORIZONTAL SECTION THROUGH MOUTH AND PHARYNX AT THE LEVEL OF THE PALATINE TONSILS. The stylopharyngeus, which is shown immediately to the medial side of the external carotid artery, and the. prevertebral muscles, are not indicated by reference lines.
part, the wall of the pharynx is related to the internal pterygoid muscles, separated from them by the levator and tensor veli palatini muscles. As each internalipterygoid passes posteriorly and downwards to its insertion, it diverges away from the pharynx, and a triangular space is left between its medial surface and the wall of the pharynx. The styloid process, and the muscles which arise from it, project downwards into this space, and lying beside them are numerous vessels and some nerves. Thus, the styloglossus and stylopharyngeus come into contact with the side wall, and, with the stylo-pharyngeus, the glosso-pharyngeal nerve. The ascending palatine and tonsillar branches of the external maxillary artery ascend in close relation to the pharyngeal wall.
The internal carotid artery lies rather further back, with the vagus, accessory and hypoglossal nerves.
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The external carotid lies more superficially, and is here separated by a considerable interval from the pharyngeal wall.
Lastly, a process of the parotid gland may insert itself on the medial aspect of the internal pterygoid, and come into contact with the pharynx.
The pharyngeal plexus of nerves lies in contact with the side wall.
Structure of the Pharyngeal Wall. The wall of the pharynx is strong and mobile; it is firmly fixed above to the base of the skull, but below that level it is not attached firmly to any surrounding structures, except to the hyoid bone and the skeleton of the larynx, and hence the inferior end can easily be displaced from side to side in the neck.
The wall is composed of a strong fibrous membrane, called the fascia pharyngobasilaris (O.T. pharyngeal aponeurosis), lined internally by mucous membrane, and covered incompletely on its outer surface by a series of three overlapping muscles, the constrictor muscles of the pharynx.
These muscles are themselves covered externally by a thin layer of fibrous tissue or fascia, which passes forwards, at its superior part, on to the surface of the buccinator muscle, and is called the fascia buccopharyngea.
External to this fascia the wall of the pharynx is in contact with loose cellular tissue by which it is connected to and separated from adjacent structures.
With the wall of the pharynx are associated several accessory muscles, viz., the muscles of the soft palate and the stylopharyngeus and pharyngo-palatine muscles, which blend with the wall but are also attached to the larynx (see p. 466).
The fibrous aponeurosis which forms the principal constituent of the pharyngeal wall is firmly attached (round the margins of the openings into the pharynx) to other structures as follows:---
Above, it blends with the periosteum covering the basilar portion of the occipital bone in front of the pharyngeal tubercle, and body of the sphenoid bone, and on each side it extends out to the angular spine of the sphenoid and the apex of the petrous part of the temporal bone.
On each side, it is attached to the structures which lie on each side of the orifices of the nose, mouth, and larynx. As it descends it gradually becomes thinner, and is
The fascia pharyngo-basilaris is particularly strong in the superior part, where there is an area on each side which is not covered by the superior constrictor muscle. This area forms the sinus of Morgagni, and here the tuba auditiva and tensor and levator veli palatini muscles pass through the wall.
Mucous Membrane of the Pharynx.-The superficial layer of the mucous membrane of the pharynx consists, in the lower part, of a stratified squamous epithelium, while in the upper or nasal portion it is, in part, composed of ciliated epithelium. In the superior part of the pharynx and in the side wall, there are found large masses of lymph tissue, constituting the pharyngeal tonsil in the roof, and the palatine tonsil on each side. The same tissue is found in considerable amount in the pharyngeal recess and on the pharyngeal portion of the dorsum of the tongue.
There are also numerous racemose glands, of the mucous type, in the walls of the pars nasalis, and in the soft palate, and in the ary-epiglottic folds.
Pharyngeal Muscles. For the details of the attachment and relations of these muscles, see pp. 464-467.
External to the pharyngeal muscles lies the fascia buccopharyngea.
The fascia pharyngobasilaris, which is thick above and thin below, and the fascia bucco-pharyngea, which is thin above and stouter below, are practically blended into one layer above, near the base of the skull, where the muscular coat is absent. Lower down they are separated by the constrictors, and become two distinct sheets. They are strengthened in the median plane posteriorly by a fibrous band descending from the pharyngeal tubercle.
Vessels and Nerves of the Pharynx.-The arteries of the pharynx are derived from—1, the ascending pharyngeal; 2, the ascending palatine branch of the external maxillary; 3, the descending palatine from the internal maxillary, with a few twigs from the dorsalis linguæ, tonsillar (of external maxillary), the artery of the pterygoid canal, and the pharyngeal branch of the internal maxillary. The veins go to the pharyngeal venous plexus, which is found between the constrictors and the bucco-pharyngeal fascia. The plexus communicates with the pterygoid plexus above and with the internal jugular or common facial vein below.
The lymph vessels of the pharynx pass chiefly to the superior set of deep cervical glands.
Those from the superior part of the posterior wall join a few retro-pharyngeal glands which are found on each side between the pharynx and the rectus capitis anterior muscle. These latter glands, which are large in the child, small in the adult, but apparently always present (Fig. 906), are of considerable clinical interest, as they often form the starting-point of post-pharyngeal abscess. For fuller details see section on Lymph Glands.
The nerves of the pharynx, both motor and sensory, are derived chiefly from the pharyngeal plexus, which is formed by branches of the vagus, glosso-pharyngeal, and sympathetic. soft palate and the neighbourhood of the palatine tonsil are supplied by the palatine branches of the spheno-palatine ganglion. The tonsil receives a branch from the glosso-pharyngeal direct The vault of the pharynx, and the region around the orifice of the tuba auditiva, as well as the orifice itself, are supplied by branches from the spheno-palatine ganglion. Finally, the internal laryngeal nerve supplies the mucous membrane of the back of the larynx, where it forms the anterior wall of the laryngeal portion of the pharynx.
The œsophagus or gullet is the portion of the digestive canal which intervenes between the pharynx above and the stomach below. With the exception of the
pylorus, it is the narrowest, and at the same time one of the most muscular parts of the whole alimentary tube.
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It extends from the termination of the pharynx, at the inferior border of the cricoid cartilage and opposite the sixth cervical vertebra, to the cardiac orifice of the stomach. opposite the eleventh thoracic vertebra Between those two points it traverses the inferior part of the neck, the whole length of the thorax, and, having pierced the diaphragm, it enters the abdomen, and immediately afterwards joins the stomach. In its course it does not adhere to the median plane of the body, but twice leaves it, and curves to the left. The first of the curvatures corresponds to the inferior part of the neck and the superior part of the thorax Aperture in diaphragm where the oesophagus projects beyond the left margin of the trachea to the exten: of or inch (4 to 6 mm.). It returns to the median plane at the level of the fourth thoracic vertebra, posterior to the aortic arch. Lower down, posterior to the pericardium, it again passes to the left, and at the same time forwards, in order to reach the oesophageal opening in the diaphragm (which is placed anterior to and to the left of the aortic opening), and it maintains this direction until the stomach is reached. It leaves the median plane at the seventh thoracic vertebra, crosses anterior to the aorta at the level of the eighth thoracic vertebra, and traverses the diaphragm at the level of the tenth.
In addition to the curvatures just described, it is also curved in the anteroposterior direction, in correspondence with
FIG. 907.-DIAGRAM TO SHOW THE COURSE OF
the form of the vertebral column, upon which it, in great part, lies.
In length it usually measures about ten inches (25 cm.).
Its breadth, where the tube is widest, varies between half an inch (13 mm. in the empty contracted condition and an inch or more (25 to 30 mm.) in the fully distended state.