We have said, that the tongue assists in the process of deglutition, and this it does chiefly by means of two appendages which we have not yet described One of these is a cartilaginous lid, nearly of a hemispherical shape, attached to the root of the tongue, and which, in the act of swallowing, covers the opening into the wind pipe. It is therefore called the epiglottis. Sec Plate XIV. Fig, 1:,..md 6. E. This pan can scarcely be said to as sist in deglutition, though, during that process, it is always in action. The other organ is more immediately subservient to deglutition. This is the os hyoides. or, as it is commonly called, the bone of the tongue. This bone has received its name from its being soaped like the letter U ; it is situated inunediatelj at toe root of the tongue, to which, and the neighbouring parts, it is closely connected by numerous and important muscles. Sec the Tables of the Bones and the Muscles. The body of this bone is seated lorwards, while its horns project backwards to the opening of the gullet. Sec Plate XI V. Fig. 5. ?, a, a. In the act ol swallowing, this bone is drawn strongly upwards, while the epiglottis is forced downwards. Thus, the opening to the gullet is en larged, and the communication between the pharynx and the wind-pipe is cut oft Several morbid appearances have been observed in the organs of deglutition. The gullet is often lound lined with a layer of coagulated lymph, arising from previous inflammation. Strictures or contractions of the gullet are not unf•equent, arising sometimes from a puckering of the mucous membrane, but more gene rally front inflammation and consequent ulceration, or from scirrhous tumours, either within the gullet, or in the neighbouring parts. Some part of the gullet has occasionally been found cartilaginous. The morbid ap pearances of the pharynx arc chiefly fungous or scirr hous tumours growing within it, and sometimes this cavity is dilated towards the gullet into a bag or pouch.
On the structure of the organs of deglutition, see Blculand's Observationes ..elizatomico-Medicx dr S'ana et Morbosa Oesophagi Structura, published at Leyden in 1785, with several coloured plates, that represent, in a lively manner, the appearance of the membranous lining of the gullet ; Biehat's ?:atop/fie Descriptive, tom. iii. p. 379.; and Cuvier's Anatomic Comparee, torn. iii. p. 366. Some good figures, illustrative of the anatomy of the gullet, are attached to a thesis, De Dysphagia, by Dr Monro tertius, published at Edinburgh in 1797.
-Organs of C'hylification In converting the food into that nutritious milky fluid called chyle, it has generally been supposed that a very complicated apparatus is necessary. Accordingly nume rous organs are described by anatomists, as •hylo-poetir -viscera, viz. the stomach, intestines, and mesentery, as more immediately concerned ; and the liver, the pan creas, the spleen, &c. as assistant chylo-ftoetic viscera. There is no doubt that all these organs, in some mea sure, concur in preparing the food for affording nourish ment to the animal system, though recent observation has shewn that the stomach is the principal organ con cerned. In the present section, we shall confine our selves to the stomach and intestines, with some of their connecting membranes. We shall describe the liver, spleen, and pancreas, under the organs of secretion.
The stomach is a large expanded portion of the ali mentary canal ; the figure of which has been compared to that of the bag of a bagpipe, being largest at one end, tapering towards the other, where it again extends a little, and ending by another contracted portion at the commencement of the small intestines. The stomach is situated at the upper part of the belly, a little towards the left side, nearly fitting the left hypochondriac region with its large extremity, stretching thence through what is called the epi•astric region, where it terminates with a curve backwards towards the spine; see Plate XIX. Fig. 9. and 11.0. Above it is connected by the o2sopha
gus, at that orifice called the cardia, with the diaphragm, and with part of the liver ; below it is united, by a par. titular membrane, to the largt st portion ol the Intes tines called colon. Its fore part is in contact with the Illuminant. of the belly next the recti muscles, and the liaise ribs ; while on the back part, it is secured by the membranes that connect the several parts of the alimen tary canal. The c =entity next the intestines has been called pylorus, because the stomach is, during diges tion, here contracted, so as to cut off, as by a gate, the communication with the bowels. Between the cardia and the pylorus there are two rounded borders or curva tures of the stomach ; one a little sterna', and sacral, which is convex, and very large, and is called the great curvature ; the other dorsal, or towards the back part, concave next the spine, and called the lesser curvature. When the stomach is empty, the greater curvature in clines towards the sacrum ; but when this cavity is dis tended ith food, the great curvature rises, and projects forward. Towards the left, the large extremity of the stomach terminates in a close pouch, considerably be yond the entrance ol the gullet.
The stomach, considered in its intimate structure, is, like the rest of the alimentary canal which we have to describe, composed of three coats, or layers ; the most peripheral or outmost of which consists of a smooth se rous membrane, formed, as w ill hereafter appear, by a reflected portion of the peritoneum. This coat is thence called the peritoneal coat of the stomach, and serves chiefly to connect this organ with the rest of the viscera, and by its Smoothness to facilitate its movements in the belly. This coat is furnished with but few nerves and blood-vessels. Within it, and connected to it by cellular substance, is a layer of muscular fibres, forming the muscular coat, to which the stomach owes its strength and power of contraction. This coat is thin, and its fibres, from being of a whitish colour, are not very dis tinct. There are, however, in the stomach, as in the gullet, two orders of muscular fibres ; one running longitudinally, in the direction of the great curvature, but rather few in number, and not very regularly dispo sed ; the others circular, more evident and numerous. These last are more properly the muscular fibres of the stomach ; the former being a continuation of the fibres of the gullet. The circular fibres arc few in number near the cardia, but gradually accumulate towards the pyierzis ; and are most remarkable at a little distance front that orifice, towards the middle of the stomach. The greater accumulation of muscular fibres at this part will be found to de-,erve particular notice, as it ex plains an important step in the process of digestion. What is properly called the third coat of the stomach, is a continuation of the mucous membrane of the guilt t, or, rather, it is a portion of that general investing mu cous membrane that lines the whole alimentary canal. It is in the stomach that this membrane first begins to assume the appearance of pl tits, or folds, which are, as we shall see, so remarkalle in some of the intestines. The folds within the stomach are, however, scarcely visible, except when this cavity is empty. Thcy are indeed merely accidi ut.a, and appear to be owing to an irregular contraction of the muscular fibres. puckering up the mucous membrane. This membrane is connected to the former coat by cellular substance. which, as we remarked in describing the gullet, has been ranked as a fourth coat, under the name of nervous. The stomach has numerous blood-vessels and absorbents, and reedit es its nerves, which arc most numerous next the cardia, from the great sympatheties and liar vagum. There arc mime mils minute glands spread over the internal membrane of the stomach, next the small curvature ; but they are scarcely to be seen in any other part.