PHARYNX. The Pharynx may be best described as a musculo-membranous bag, situated between the larynx and guttural pouches, anteroinferiorly opening into the fauces, postero-superiorly continuous with the esophagus. Hitherto the pharynx has generally been described as consisting of three pairs of constrictor muscles and three pairs of dilator muscles; but I think I shall be able to shew that such an arrangement is not correct. The three pairs of dilator muscles usually given are the hyo-pharyngeus, stylo-pharyngeus, and palato-pharyngeus; but, on a careful dissection, it will be found that the arrangement and action of these muscles are widely different from that which has generally been taught. In order to render the subject intelligible, and to facilitate description, I have given a rough diagram; but ere I refer to it, perhaps I had better give the origin and insertion of the different muscles belonging especially to the pharynx. Dilators, two pairs. The Hyo-Pharingeus arises from about the middle of the internal side of the greater cornua of the os hyoides, takes a slanting direction downward and forward, and is inserted into the superior edge of the mouth of the pharynx. The Palato-Pharyngeus (improperly named) is a mass of disgregated muscular fibres, spread over the anterior part of the membrane lining the fauces. Some of the fibres are slightly attached to the free edge of the velum palati; the remaining portion of the muscle blends with its fellow of the opposite side there is also a small portion extending backward beneath the anterior constrictor muscle of the pharynx. The Constrictor Muscles. Of these there are three pairs; and those more particularly contribute to form the pharynx : The Constrictor Anticus arises from the spur-like process of the os hyoides, covering its articulation with the thyroid cartilage. The muscle then unites with its fellow of the opposite side by a ligamentous line. The Constrictor Medius arises from the alæ of the thyroid cartilage, and this muscle unites with its fellow as the preceding. The Constrictor Posticus arises from the edge and lateral protuberance of the cricoid cartilage, and, as the former muscles, unites with its fellow of the opposite side, likewise blending its fibres with the superior portion of the esophagus. I shall enter upon the action of these muscles more particularly when I come to the physiology of deglutition. There are yet two pairs of muscles left to speak of; and these I do not believe have any thing to do with either the contraction or dilatation of the pharynx: so that, truly, there are only five pairs of muscles directly acting upon, or strictly belonging to, the pharynx. The two pairs of muscles I am about to describe are generally known as the stylo-pharyngeus, which I propose calling the CONSTRICTOR FAUCES ANTICUS; and the pterygo-pharyngeus, generally described as a part of the palato-pharyngeus; this I propose to call the CONSTRICTOR FAUCES POSTICUS. The Stylo Pharingeus, or Constrictor Fauces Anticus, arises from the styloid process of the petrous temporal bone; runs along the edge of the eustachian tube, to which it is attached; passes over the anterior part of the fauces, and there unites with its fellow of the opposite side. (See woodcut, fig. 9.) The Pterygo Pharyngeus, or Constrictor Fauces posticus, arises from the arch or hollow of the pterygoid bone, slants obliquely backwards over the posterior part of the fauces, and also unites with its fellow of the opposite side. (See woodcut, fig. 8.) The action of these I shall also be better able to illustrate when considering the physiology of deglutition. The pharynx receives its nerves by branches given off from the pneumo-gastric, glosso-pharyngeus, and sympathetic. Its arteries are principally derived from the sub-maxillary artery, and its veins empty themselves into the sub-maxillary veins. Having now hastily glanced at the anatomy of the pharynx and fauces, I will proceed to the consideration of the physiology of deglutition. The subjoined sketch, however, may serve to elucidate that which might otherwise appear complicated. In passing in review the various and complicated movements dependent on, or which are called into activity by, the process of deglutition, or, in other words, the transit of food from the mouth to the stomach, it will be easy to perceive that the limits of a thesis like the present will, of necessity, preclude the possibility of my entering upon a detailed illustration of the individual action of each particular part: indeed, it would involve the consideration of a most numerous and intricate complication of muscles; and, even had I time and space, ability to unravel so tangled a net-work of junctions would, I fear, be wanting; therefore I shall only at tempt an outline of the process, referring those who may wish to complete the picture to some of the popular physiological works. Deglutition is the act of transferring any substance from the mouth to the stomach; but my remarks now are to be taken as relating to the transmission of food after mastication and insalivation. The former of these operations consists in the mechanical reduction of the food to a proper consistence; the latter, the commingling of it with a liquid called saliva, secreted by glands especially appropriated to that function. The process of deglutating the mass so prepared may be divided into four distinct periods or actions; the first comprehending its passage over the tongue to the fauces, the second from the fauces into the pharynx, the third from the pharynx into the esophagus, and the fourth from the esophagus into the stomach. The first of these is purely an act of volition, it being accomplished solely in accordance with the will of the animal. The food, when sufficiently masticated, is collected from all parts of the mouth, and placed on the surface of the tongue: the apex or tip of the tongue is now raised against the palate, and by its peculiar movements, aided by the bars (which readily allow the food to pass upwards and backwards, but offer a considerable obstacle to its return towards the lips), the food is conveyed to the summit of the dorsum of the tongue, just about the termination of the bony palate. Here it is the second action commences: this, I should say, is partly voluntary, and partly involuntary; in fact, a mixed action and it must be obvious that a very different must now be made, in order to propel the palate forwards, there being no hard unyielding substance for the tongue to press against, or bars to prevent its falling down towards the lips. A slight inspection of the diagram (letter a) will shew, much more clearly than mere description can, that the tongue, posterior to that part I have called its summit, forms an inclined plane into the fauces, being roofed over (if I may use the term) by the velum palati. This velum palati is, as I have before said, covered with a large glandular mass: whether the secretion from it be a salivary or a mucous one, I know not; but, be it what it may, the pressure of the pellet squeezes out its contents, and by that means the pellet is rendered smooth, and thus glides down over this inclined plane into the fauces. Co-existent with this gliding down of : arrangement the pellet, the larynx is raised or swung up between the os hyoides, and also drawn slightly forward, the tongue at the same time being drawn slightly backward: the epiglottis is now shut down upon the glottal opening (which closure I am inclined to think is accomplished partly by the mutual approach of the larynx towards the tongue and the tongue towards the larynx, and partly by the mechanical pressure of the food against the epiglottis). We have now to see how the pellet is prevented from entering the nostrils, there being a free communication between the nose and the fauces; and here again I must refer you to the sketch. Fig. 8 and 9 are the two muscles I have proposed to call the anterior and posterior constrictors of the fauces, and whose actions I have said I should be able to demonstrate. Their use must now be obvious. When the pellet has reached the bottom of this inclined plane, these muscles, contracting, approximate the sides of the fauces, which their peculiar crucial arrangement, as seen in the sketch, admirably adapts them for effecting in fact, the action of these muscles is precisely analogous to the peculiar species of sphincter muscle found at the cardiac extremity of the stomach. : It would be scarcely possible to conceive that these muscles would completely close the orifice as an orbicular muscle would; but this is provided for and accomplished by the elevation of the velum plati, or rather its free edge, which is raised by the contraction of the tensor palati muscles, the singular arrangement of which has already been pointed out; so that by the contraction of these muscles, aided by the velum palati, the pellet of food is effectually and beautifully prevented from entering the nostrils. The only passage now left for this pellet of food is that of the pharynx, the entrance of which is held open by two pairs of muscles already described. (See sketch, fig. 6, 7.) There it is immediately grasped by the anterior constrictor (fig. 1), which muscle by the slightest tactile impression is instantly stimulated to powerful contraction, as indeed are all the muscles strictly belonging to the fauces and pharynx. We cannot will that we would swallow; there must be a something of sufficient substance to stimulate or touch these muscles, or the act of deglutition could not be excited. This brings me to the third action, which must obviously be a purely involuntary one, viz. that act by which the food is conveyed through the pharynx into the esophagus. As soon as the pellet of food has |