The same observations will apply to the structure of the alimentary canal generally.

15. The villous, or mucous membrane has a whitish-red appearance, and presents a singular velvet-like appearance, from which it has derived its name: not being elastic, it has numerous folds, or rugae, which supply this deficiency, and serve to accommodate the capacity of the stomach to the bulk of its contents; and, at the same time, to retain the aliment until it is duly elaborated. It is usually lined with a mucous matter, especially in its splenic extremity: it also contains many follicles; and near the pylorus are to be seen several glands, to which is assigned a peculiar office to be hereafter described. At this spot also, the mucous membrane thickens, and forms a circular fold, which perforins the office of a valve; a fibrous dense tissue is also here found, which some authors have called the pyloric muscle. The stomach is abundantly vascular; indeed it may be observed, that few structures receive so much blood as this organ: four arteries, three of which are considerable, are exclusively devoted to its service; and their several branches communicate most freely with each other in all directions by innumerable anastomoses: and, being tortuous, they can thus accommodate themselves to the full and empty states of the cavity.

Nor are its nerves less numerous: they are composed of the eighth pair, and a great many filaments proceeding from the solar plexus of the great sympathetic.

16. Notwithstanding the important discoveries of Sir Charles Bell, there still remains some obscurity with respect to the influence of each particular nerve on the functions of the stomach. The par-vagum, or eighth nerve of Willis, (the pneumo-gastric nerve of the modern physiologists of France,) would appear, from various experiments, to be that which imparts to the stomach its peculiar sensibilities, and at the same time to connect it in a necessary tie of sympathy with the heart and respiratory organs; thus is it that a blow on the stomach "doubles up" the bruiser, and occasions that gasping and crowing which sufficiently indicate the course of the shock through the branches of the pneumo-gastric nerves; a little more severe and the blow is fatal. In like manner may we explain the irritation of the lungs and palpitation of the heart so often excited by gastric derangement; nor can the physiologist, unacquainted with these relations, assign any cause for certain disturbances of the stomach being accompanied by hiccup, vomiting, sneezing, etc.

17. The nerves derived from the great sympathetic minister to its other functions, and although it may be difficult to assign to each nerve the duty with which it is charged, of this we may be assured, that through their combined agency, the stomach is brought into communion with every part of the machine.

18. The duodenum convprehends that range of small intestine which commences at the pylorus, and extends for about twelve inches; and so important are the changes which the aliment undergoes in its cavity, that many authors have regarded it as entitled to the appellation of a second or accessory stomach; and I shall, hereafter, have occasion to state, that many diseases which have been erroneously attributed to the stomach, derive their origin from the functional aberrations of this intestine; a fact which renders a knowledge of its structure and situation of great importance to the pathologist. Unlike the stomach, which may be said to be comparatively loose and floating in the abdominal cavity, it is secured in its position by various attachments, and the manner in which it is protected strongly evinces the importance of its functions. The practitioner should ever keep in mind the position and bearings of this intestine; for patients, directed by their own uneasy feelings, will frequently trace, with most anatomical accuracy, the course of the duodenum with their finger, from the stomach to the loins on the right side, and back again across the abdomen to the umbilicus.

The duodenum, at its commencement, turns backwards and downwards for a short way; it then turns towards the right kidney, to the capsule of which it is more or less attached; it here forms a sacculated angle, and in this depending part, the ducts for conveying the pancreatic and biliary secretions enter the intestine: it now ascends from the right to the left, just before the aorta and the last vertebrse of the back; it continues this direction from thence obliquely forward by a slight curvature, and makes its exit through the ring in the mesentery. Its mucous membrane, which presents many villi, and a great number of follicles for the secretion of its own peculiar fluid, forms irregular circular folds, termed "Valvules conniventes," which increase the surface of the intestine, while they prevent the too rapid passage of its contents. It is furnished with nerves from the ganglions of the great sympathetic; and it is also abundantly supplied with blood-vessels. It is impossible to view all the arrangements of this organ, without being satisfied that nature was anxious to limit its motions; and a little reflexion will convince us of the great importance of such a provision: Dr. Yeats, in his valuable paper on the duodenum1, which is published in the sixth volume of the Transactions of the College, has alluded to this fact in a very pointed manner.

It is evident that, had this intestine been loose and floating, the food might have passed too rapidly through it: it might also have drawn the small end of the stomach out of its proper situation; and there would have been a constant disposition in the food to pass out of the stomach into the duodenum, upon every relaxation of the pylorus: besides which, had it been less confined, and consequently subject to greater distention, a regurgitation might have taken place into the ductus communis, from an alteration in that obliquity of its direction, which now so securely guards against such an occurrence. Dr. Fordyce, in noticing the fact of the peritonaeum being wanting on the back of the duodenum, most erroneously concludes, that this was ordained with a view of allowing a greater distention than can take place in the lower intestines: had such been the design of nature, she certainly would not have discarded so highly elastic a membrane, and attached the back of the duodenum to the vertebras.

1 Some Observations on the Duodenum; with plates descriptive of its situation and connexions. Extracted from the Gulstonian Lectures, by G. D. Yeats, M.D., etc.

19. The Jejunum

The precise point at which the duodenum terminates, and. the jejunum commences, cannot perhaps be accurately defined; but this latter intestine is generally considered as beginning where the mesentery takes its rise. It appears to have derived its name from the fact of its usually being found empty; probably from its more rapid powers of absorption.

20. The Ilium

The Ilium is the continuation of the jejunum, and is the last division of the small intestine; it is said to have derived its name from the manner in which it is coiled up by the mesentery. Its parietes are thinner than those of the preceding portion of the canal; and this circumstance, together with the deep yellow colour of its contents, impart to it an appearance very distinct from that of the duodenum.

21. The large intestines exceed the others in diameter, but are less considerable in length; in structure they also differ materially from the small intestines: their mucous membrane does not present that villous appearance of which we have spoken; but is, on the contrary, smooth: the number of follicles is also less, and it is supplied with much fewer arteries, veins, and nerves.