Organs of Deglutition The organs employed in swallowing the food are chiefly the pharynx and gullet, assisted by the tongue and soft palate.
The pharynx is a funnel-shaped cavity, situated be hind the soft palate, in that aperture called by anatomists the isthmus faucium, or opening of the throat. It is pro perly the commencement of that long, irregular, winding passage, called the alimentary canal, which traverses all the cavities of the body, from the mouth downwards. It is this organ which receives the food from the mouth, and conveys it into the gullet. The pharynx is bounded above by the basilar process of the occipital bone; on the fore part by the cavities of the nose, and by the la rynx ; behind by the bodies of the cervical vertebra;, and below it ends in the gullet. It is in a manner sus pended from the pterygoid processes of the sphenoid bone, and from the horns of the os hyoides and thyroid cartilages. Strictly speaking, it forms only hall a cavity, being imperfcet on the fore part, where it serves as a common receptacle, both to the food that is about to pass into the gullet, and the air that enters the wind pipe. Its internal surface is more extensive than its ex ternal, as it consists of membranous productions from the pillars of the soft palate, and other neighbouring parts. This internal membrane is not of so deep a red as that of the mouth, though of a higher colour than tae membrane that lines the gullet ; and this difference ol colour forms one or the most distinct marks of separa tion between the gullet and what is properly called the pharynx. Within this membrane are numerous mucous glands, w ith excretory ducts opening into the cavity of the pharynx. The external or peripheral surface of the pharynx is composed of numerous muscular fibres, con stituting three distinct portions, which have been culled the constrictor muscles of the pharynx, and running transversely with different deg' ces of inclination, ac cording to their points of attachment.
The Oesophagus, gala, or gullet, is a long canal. partly fleshy, and partly muscular, that leads from the pharynx to the stomach. It is commonly said to be cy
lind•ical, though in its ordinary, inactive state, its sides arc applied closely to each other. It passes through the chest, close to the bodies of the vertebra: of the neck and back, within the doubling of the mcdiatinum ; but it does not pursue a straight direction. Until it an ives at the lower part of the neck, it runs in the direction of the mesial line, but here it inclines insensibly to the left, preserving this direction till it arrives at that part of the chest where the windpipe divides and enters the lungs, when it resumes its former mesial course. On the fore part the gullet is closely connected with the larynx, the thyroid gland, the left side of the windpipe, and the inferior thyroid artery on the left side ; behind to the bodies of the cervical and dorsal vertebra:, the aorta, and the thoracic duct ; and on the sides it runs along with the jugular veins and the carotid arteries. It is composed principally of two layers, a peripheral muscular layer, and a central membranous lining. The former is made up of two sets of muscular fibres, of which those on the peripheral surface run in a longitu dinal direction, while the others run transversely or cir cularly. The membranous lining differs little from that of the pharynx, except that it is of a whiter colour. Between the muscular coat and the mucous membrane there is a quantity of cellular substance, which has been termed by some anatomists, the nervous coat ; and with in this, next the mucous membrane, lie numerous glands, are more thickly set at that part of the gullet where it joins the stomach. These glands secrete a lubricating fluid, which is poured through correspond ing orifices into the cavity of the tube, and facilitates deglutition. The gullet is well supplied with nertes, both from the eighth pair and the intercostals, and with numerous absorbent vessels. Its arteries will be noticed hereafter.
The gullet is susceptible of great dilatation, as ap pears from the large masses which occasionally pass through it.