The pharynx is surrounded by muscular fibres which have been collected into three distinct muscles on either side, and named, from their action, constrictors ; these may be considered as intrinsic: two other muscles on either side are inserted into its walls, and are extrinsic as not belonging so exclusively to it. The constrictor muscles are membraniform, spreading as thin muscular laminm around the sides and back part of the pharynx, and have a common insertion into a posterior median raphe: they partly overlap each other from below upwards, so that the inferior constrictors alone can be wholly examined without inter fering with the rest, and are invested on their outer surface with a dense fascia: they arise by numerous and distinct points of attachment, which gave occasion to their being divided originally into several muscles, each with its appropriate name given according to its par ticular origin : these are now reduced to three on each side, and arranged into superior, middle, and inferior.
Constrictor pharyngis inferior.* — This muscle is the thickest and strongest of the set, has an irregular quadrilateral outline, and is situated at the lower part of the pharynx : it derives its origin from the cricoid and thyroid cartilages by two slips: the one, triangular and fleshy, arises from the side of the cricoid car tilage between the origins of the crico-arytenoi deus posticus and crico-thyroideus muscles : from the latter it occasionally receives a few fibres : the other, broader and more extensive, lies on the ala of the thyroid cartilage, and arises from the two tubercles, which the ala presents on its external surface, and from a tendinous structure that stretches obliquely from one tubercle to the other : it is here blended with the attachments of the sterno thyroid and thyro-hyoid muscles : it also em braces the inferior cornu of the thyroid carti lage : from these points it spreads round the side and back of the pharynx to the posterior median raphe, into which it is inserted con jointly with the muscle from the opposite side ; the fibres pa.ss in different directions : the su perior are longer and pursue a more oblique course upwards, while the nearer they are ex amined to the lower margin of the muscle, the shorter and less oblique they become, and at length assume nearly a transverse direction. The origins of the inferior constrictor muscle are concealed by the thyroid gland and sterno thyroid muscle: it is in relation laterally to the sheath of the carotid vessels, and posteriorly to the cervical vertebrx and deep muscles of the neck : its internal surface is applied partly upon the mucous membmne and the terminal fibrei of the stylo-pharyngeus and palato-plia ryngeus muscles, hut to a greater extent upon the middle constrictor muscle: the oblique upper margin extends as high as the middle of the pharynx and close by its thyroid attach ment allows the superior laryngeal nerve to pass beneath it : the circular fibres of the ceso phagus are continued frorn its lower margin, but distinguished by their greater delicacy and paler colour: close to the cricoid cartilage the inferior or recurrent laryngeal nerve slips be neath its lower margin. Some of the lower fibres have occasionally been noticed to arise from the first ring of the trachea.
Constrictor pharyngis matins. is of a trian gular forni, fixed by its apex to the hyoid bone and by an extensive base to the median raphi: behind : its origin is received into the angle formed by the greater and smaller cornua of the os hyoides, to which processes the muscular fibres are attached as well as to the lower part of the stylo-hyoid ligament: the origin extends along the greater cornu quite to its posterior extremity, and is concealed by the hyo-glossus muscle, the lingual artery intervening : from this contracted commencement the middle con strictor spreads widely over the back of the pharynx, the superior fibres obliquely ascend ing towards the basilar process of the occipital bone, to the spine of which they are connected through the medium of the raphe, the muscle itself rarely reaching so high ; the middle fibres take a more or less transverse direction, while the inferior descend under cover of the inferior constrictor: the whole muscle is inserted, with its fellow from the opposite side, into the raphe. After emerging from beneath the hyo
glossus it is related to the external carotid ar tery and superior laryngeal nerve laterally, and to the vertebral column behind: by its internal surface it overlaps the superior constrictor, and is applied upon the stylo- and palato-pharyngei muscles and the mucous membrane. Near the great cornu of the hyoid bone the stylo-plia ryngeus muscle insinuates itself beneath its upper border, separating it from the superior constrictor.
Constrictor pharyngis superior,t quadrila teml in shape and complicated from its very numerous attachments. The fibres of this muscle are paler and it is altogether thinner than the two former: it arises, firstly, by short tendi nous fibres from the lower half of the posterior edge of the internal pterygoid plate and its ha mular process; secondly, from an aponeurosis described as the inter- or pterygo-maxillary liga ment common to it and the buccinator muscle, and which stretches from the inner pterygoid plate to the posterior extremity of the alveolar border of the inferior maxillary bone; thirdly, from the back part of the mylo-hyoid ridge; and, lastly, is said to arise from the side of the tongue near its base : this lingual origin is con sidered by some anatomists as a part of the genio-hyo-glossus muscle :* arising thus, the superior constrictor winds round the pharynx and is inserted into the cephalo-pharyngeal aponeurosis, upon which it is placed, and joins with its fellow from the opposite side at the median raphe. The superior fibres make a semicircular sweep upwards tovvards the spine of the basilar process, to which they are con nected by the raphe: the rest pass more trans versely to their insertion and are partially over lapped by the middle constrictor : between the upper border of this muscle and the base of the skull the pharyngeal aponeurosis is left un covered by muscular fibres. The superior constrictor corresponds posteriorly to the cer vical vertebrze, and is separated laterally from the internal pterygoid by a triangular space which is occupied by the internal carotid ar tery, internal jugular vein, and the eighth and ninth pairs of nerves : the stylo-pharyngeus muscle is also related to its outer side before it descends beneath the middle constrictor: by its internal surface it is applied upon the levator palati and palato-pharyngeus muscles, the mu cous membrane and the tonsil.