Constrictor Inferior. Constrictor Superior.
Constrictor Medius. Stylo-pharyngeus.
Palato-pharyngeus.

Dissection. In order to examine the muscles of the pharynx, cut through the trachea and oesophagus just above the sternum, and draw them upwards by dividing the looso areolar tissue connecting the pharynx with the front of the vertebral column. The parts being drawn well forwards, the edge of the saw should be applied immediately behind the styloid processes, and the base of the skull sawn through from below upwards. The pharynx and mouth should then be stuffed with tow, in order to distend its cavity and render the muscles tense and easier of dissection.

The Inferior Constrictor, the most superficial and thickest of the three, arises from the side of the cricoid and thyroid cartilages. To the cricoid cartilage it is attached in the interval between the crico-thyroid, in front, and the articular facet for the thyroid cartilage behind. To the thyroid cartilage, it is attached to the oblique line on the side of the great ala, the cartilaginous surface behind it, nearly as far as its posterior border, and to the inferior cornu. From these attachments, the fibres spread backwards and inwards, to be inserted into the fibrous raphe in the posterior median line of the pharynx. The inferior fibres are horizontal, and overlap the commencement of the ossophagus; the rest ascend, increasing in obliquity, and overlap the Middle constrictor. The superior laryngeal nerve passes near the upper border, and the inferior, or recurrent laryngeal, beneath the lower border of this muscle, previous to their entering the larynx.

Relations. It is covered by a dense cellular membrane which surrounds the entire pharynx. Behind, it lies on the vertebral column and the Longus colli. Laterally, it is in relation with the thyroid gland, the common carotid artery, and the Sterno-thyroid muscle. By its internal surface, with the Middle constrictor, the Stylo-pharyngeus, Palato-pharyngeus, and the mucous membrane of the pharynx.

The Middle Constrictor is a flattened, fan-shaped muscle, smaller than the preceding, and situated on a plane anterior to it. It arises from the whole length of the upper border of the greater cornu of the hyoid bone, from the apex of this cornu by a tendinous origin, from the lesser cornu, and from the stylo-hyoidean ligament. The fibres diverge from their origin in various directions; the lower ones descending and being overlapped by the inferior constrictor, the middle fibres passing transversely, and the upper fibres ascending to cover in the Superior constrictor. It is inserted into the posterior median fibrous raphe, blending in the middle line with the fibres of the opposite muscle.

Relations. This muscle is separated from the Superior constrictor by the glosso-pharyngeal nerve and the Stylo-pharyngeus muscle; and from the inferior constrictor, by the superior laryngeal nerve. Behind, it lies on the vertebral column, the Longus colli, and the Rectus anticus major. On each side it is in relation with the carotid vessels, the pharyngeal plexus, and some lymphatic glands. Near its origin, it is covered by the hyo-glossus, from which it is separated by the lingual artery. It covers in the Superior constrictor, the Stylo-pharyngeus, the Palato-pharyngeus, and the mucous membrane.

The Superior Constrictor is a quadrilateral plane of muscular fibres, thinner and paler than those of the other Constrictors, situated at the upper part of the pharynx. It arises from the lower third of the margin of the internal pterygoid plate and its hamular process, from the contiguous portion of the palate bone and the reflected tendon of the Tensor palati muscle, from the pterygo-maxillary ligament, from the alveolar process above the posterior extremity of the mylo-hyoid ridge, and by a few fibres from the side of the tongue in connexion with the Genio-hyo-glossus. From these points, the fibres curve backwards, to be inserted into the median raphe, being also prolonged by means of a fibrous aponeurosis to the pharyngeal spine on the basilar process of the occipital bone. Its superior fibres arch beneath the Levator palati and the Eustachian tube, the interval between this border of the muscle and the basilar process being deficient in muscular fibres, and closed by fibrous membrane.

Relations. By its outer surface, behind, with the vertebral column. On each side, with the carotid vessels, the internal jugular vein, the three divisions of the eighth and the ninth nerves, the Middle constrictor which overlaps it, and the Stylo-pharyngeus. Internally, it covers the Palato-pharyngeus and the tonsil and is lined by mucous membrane.

The Stylo-pharyngeus is a long, slender muscle, round above, broad and thin below. It arises from the inner side of the base of the styloid process, passes downwards and inwards to the side of the pharynx between the Superior and Middle constrictors, and spreading out beneath the mucous membrane, some of its fibres are lost in the Constrictor muscles, and others joining with the Palato-pharyngeus, are inserted into the posterior border of the thyroid cartilage. The glosso-pharyngeal nerve runs on the outer side of this muscle, and crosses over it in passing forward to the tongue.

Relations. Externally, with the Stylo-glossus muscle, the external carotid artery, the parotid gland, and the Middle constrictor. Infernally, with the internal carotid, the internal jugular vein, the Superior constrictor, Palato-pharyngeus and mucous membrane.

Nerves. The muscles of this group are supplied by branches from the pharyngeal plexus and glosso-pharyngeal nerve; and the Inferior constrictor, by an additional branch from the external laryngeal nerve.

Actions. When deglutition is about to be performed, the pharynx is drawn upwards and dilated in different directions, to receive the morsel propelled into it from the mouth. The Stylo-pharyngei, which are much farther removed from one another at their origin than at their insertion, draw upwards and outwards the sides of this cavity, the breadth of the pharynx in the antero-posterior direction being increased, by the larynx and tongue being carried forwards in their ascent. As soon as the morsel is received in the pharynx, the elevator muscles relax, the bag descends, and the Constrictors contract upon the morsel, and convey it gradually downwards into the oesophagus. The pharynx also exerts an important influence in the modulation of the voice, especially in the production of the higher tones.

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