The muscular layer thus formed round the pharynx is of varying thickness, the greatest strength prevailing behind the buccal cavity, where the inferior constrictor, in itself the strongest of these muscles, overlaps the middle: on the other hand, there is but little occa sion for muscular action behind the nasal fossm, so we find, in accordance with this circumstance, a greater delicacy in the fibres of the superior constrictor and a defici ency of muscle altogether higher up: pro bably, also, the overlapping of these muscles from below upwards and the oblique direction of many of their fibres have reference to the downward passage of the food. The margins of the constrictors, as these muscles lie on each other, are not very distinct, particularly towards the back part of the pharynx. Additional mus cular slips have occasionally been observed by different anatomists, which may be briefly no ticed :-1. fibres from the petrous process of the temporal bone to pass downwards and back walds ; 2. from the basilar process directed inwards ; 3. from the internal pterygoid plate and hamular process directed downwards and inwards ; 4. from the spinous process of the sphenoid and from the cartilaginous portion of the Eustachian tube.
Use—Besides constricting the cavity of the pharynx, the inferior and middle constrictors can raise the larynx and carry it backwards, the latter through the medium of the os hyoides.
The extrinsic muscles of the pharynx are two on either side, the stylo- and palato-pharyngei.
Stylo-pharyngens.—This is a long slender muscle, broader below than above, and arises from the inner side of the styloid process at its base, and from the neighbouring part of the vaginal process : it descends inwards and for wards towards the greater cornu of the os hyoides, and expanding insinuates itself be neath the upper edge of the middle constrictor muscle to be applied upon the mucous mem brane of the pharynx : it is inserted with the palato-pharyngeus into the posterior border of the thyroid cartilage : soon after its origin it passes with the stylo-glossus muscle between the external and internal carotid arteries, lying upon the latter and the internal jugular vein : a particular feature in this muscle is its close relation to the glosso-pharyngeal nerve, which winds round its lower border from behind for wards: as it descends, its next relation is the side of the superior constrictor, and passing between it and the constrictor medius it is applied upon the mucous membrane of the pharynx.
Use.—The stylo-pharyngei raise and widen the pharynx, preparing it for the reception of the food : they are important muscles in deglu tition : the larynx is also raised by them.
Palato-pharyngeus.—This muscle will be again referred to as belonging to the palate: its fibres are contained in the fold of mucous membrane known as the posterior pillar of the fauces : it expands upwards to the soft palate, and downwards to the pharynx under the supe rior constrictor : it descends to spread its fibres on the mucous membrane, and is inserted with the stylo-pharyngeus into the posterior border of the thyroid cartilage.
2. General review of the attachments of the pharynx.—By referring to the foregoing de scriptive anatorny of its aponeurosis and mus cles, the pharynx will be seen to form from one-half to two-thirds of a vertically elongated cylinder, open in front ; and although before terminating, the interior of the pharynx is con verted into a complete canal, it is so only by the relation of a totally distinct organ, viz. the larynx. Descending perpendicularly from the base of the skull to the lower border of the cricoid cartilage, the pharynx is applied evenly to the anterior aspect of the bodies of the cer vical vertebr and deep muscles of the neck, having a remarkably loose areolar tissue inter vening, important as preserving to it a perfect freedom of motion, while, by its anterior edges, it is fixed to the internal pterygoid plates, to the pterygo-maxillary ligaments, by means of which it is continuous with the lateral walls of the mouth, to the inferior maxillary bone, the sides of the tongue and cornua of the os hyoides, thus forming behind the nasal and buccal cavi ties a large pouch, whose parietes being con stantly strained apart by these attachments, preserve a perfectly free cavity, a circumstance of considerable importance with reference to the continual passage of air to and from the respiratory apparatus : continuing downwards, the pharynx next embraces the sides of the thyroid and cricoid cartilages, but as there is no longer occasion for this tension of its walls, they become flaccid, and are loosely applied to the posterior surface of the larynx, and so con tinued into the (esophagus : if examined frorn behind, the pharynx is seen to be of great breadth at the base of the skull, but narrows until opposed to the buccal cavity, where it again widens to contract somewhat abruptly at its termination : its lateral relations to the ca rotid vessels and nerves of the neck have been considered in the descriptions of the constrictor m uscles.
3. The cavity and its openings.—The interior of the pharynx exhibits a cavity of considerable size, which is continuous with those of the nasal fossw and mouth anteriorly and the canal of the (esophagus below. To study the varying dimensions of this cavity and the different openings which communicate with it, the pha rynx must be slit up posteriorly and in the median line ; its greatest breadth is behind the mouth, the buccal portion, which may be mea sured by the interval between the posterior ex tremities of the alveolar border of the lower jaw, and is rather more than tvvo inches ; thence narrowing upwards, the internal pterygoid plates will by their distance from each other, which is about one inch, give the diameter of the cavity at its nasal portion, while the distance between the posterior edges of the alw of the thyroid cartilage will denote its breadth at the inferior or laryngeal portion : the antero-poste rior diameter can vary but little, in consequence of the relation which the vertebral column has to the pharynx behind: during the act of deglu tition these measurements are of course altered, but there is much less change of form in the upper or nasal portion of the cavity than in the rest of its extent. Dropping into the cavity from before backwards and from above down wards is the velum palati with the uvula de pending from the centre of its posterior border : above this moveable curtain are seen the poste rior openings of the nose with its median sep tum, the vomer : these are situated between the internal pterygoid plates, extend upwards to the base of the skull, and are limited below hy the velum ; they are quadrilateral in their outline and continued into the upper part of the pharyngeal cavity ; a little way within the nasal fossx and along their outer walls are seen the meatuses of the nose and the posterior edges of the inferior turbinated bones; pro longing these latter backwards by an imaginary line, we are brought to the openings of the Eustachian tubes; they are two narrow ellipti cal fissures, their long diameters, about three eighths of an inch, directed from above down wards, and situated one on either side of the pharynx above the soft palate, and impinging the posterior edges of the internal pterygoid plates ; they look forwards and inwards towards the inferior and middle meatuses of the nose, and are marked by prominent and rounded margins internally; an accurate knowledge of their relation to the nasal fossm is of pmctical use in directing a probe or syringe into their canals ; behind the openings of the Eustachian tubes are the longitudinal sulci which lead up wards and backwards to a cul-de-sac that occu pies the angle formed by the sudden bending forward of the aponeurosis of the pharynx ; below the velum is the posterior constricted aperture of the mouth, which will be again referred to in the description of the soft palate ; it is limited above by the velum, below by the base of the tongue, and laterally by the poste rior pillars of the fauces ; the uvula depending from the velum centrally gives it a double arched outline above, but it is capable of as suming changes of form by the varied move ments of its boundaries, which are especially concerned in deg,lutition ; below the isthmus faucium and behind the base of the tongue is the superior aperture of the larynx, surmounted in front by the epiglottis ; it is a triangular opening, the base directed forwards, and it has also an oblique diiection from above down wards and from before backwards ; it is gene rally completely closed during deglutition by the epiglottis being forced down upon it ; on either side of the posterior surface of the larynx, between the thyroid and cricoid cartilages, are two gutters which lead downwards to the (esophageal opening of the pharynx; this open ing has its long diarneter from side to side in the flaccid state of its walls, but assumes a circular form when distended by the passage of food through it.