volutions in the abdominal cavity. They are attached to the vertebral column by folds of peritoneum called mesentery; and according to the length of these folds or duplicatures the intestine is bound down, or floats in the abdominal cavity. Their structure is nearly alike throughout: a mucous membrane lines them: immediately without this is a muscular coat; and, externally, a serous coat, formed by a prolongation of the peritoneum. The mucous membrane is soft and velvety, and is the seat of a similar secretion to that of other membranes of the same class. The muscular coat is composed of two planes of fibres, so united that they cannot be separated,-the innermost consisting of circular, and the outermost of longitudinal fibres, the arrangement of which differs in the small and large intestines. The serous or peritoneal coat receives the intestine between two of its laminæ, which, in their passage to it, form the mesentery. The serous coat only comes in direct contact with the intestine at the sides and forepart. Behind, or on the mesenteric side, is a vacant space, by which the vessels and nerves reach the intestine. These form their first network between the serous and muscular coats; their second, between the muscular and mucous.

Between the upper four-fifths of the intestinal canal, and the lower fifth, there is a well-marked distinction; not only as regards structure and magnitude, but function. This has given occasion to a division of the canal into small and large intestine; and these, again, have been subdivided in the various modes that will fall under consideration. As the small intestine fills so large a portion of the intestinal canal, its convolutions occupy considerable space in the abdominal cavity, - in the middle, umbilical, and hypogastric regions, and terminate-in the right iliac region-in the large intestine (see Fig. 210). Its calibre differs in different parts; but it may be regarded on the average as about one inch. It is usually divided, arbitrarily, into three parts;-duodenum, jejunum, and ileum. The duodenum is so called, in consequence of its length having been estimated at about twelve fingers' breadth. It is larger than the rest of the small intestine; and has received, also, the name of second stomach, and of ventriculus succen

turiatus. It is more firmly fixed to the Longitudinal Section of the Upper body than the other intestines; and does

VOL. I.-34

Part of the Jejunum extended under

water.

not, like them, float loosely in the abdomen. In its course to its termination in the jejunum, it describes a kind of Italic c, the concavity of which looks to the left. From this shape it has been separated into three portions;-the first situate horizontally beneath the liver: the second descending vertically in front of the right kidney; and the third in the transverse mesocolon. Its mucous membrane presents a number of circular folds or rugæ, very near each other, which have been called val

Muscular Coat of the Ileum.

1, 1. Peritoneal coat. 2. A portion of this

coat turned off and showing a portion of the longitudinal fibres of the muscular coat ad

vulæ conniventes. (Figs. 230 and 231.) By some anatomists, however, this name is not given to the irregular rugæ of its mucous coat; but to those of the lining membrane of the jejunum. The valvulæ are not simple rugæ, passively formed by the contraction of the muscular coat. They are dependent upon the original formation of the mucous membrane; and are not effaced, whatever may be the distension of the intestine. On and between these duplicatures, the different exhalant and absorbent vessels are situate, forming, in part, the villi of the intestine, which are from a quarter of a line to a line and two-thirds in length. These villi give to the membrane a velvety appearance, and are not simply composed of exhalants and absorbents, but of nerves; all of which are distributed on an areolar and perhaps erectile tissue. In its healthy state, when successfully injected, the membrane appears to consist almost entirely of a cribriform intertexture of veins. It was formerly believed, that the villi are not supplied with blood vessels. In each villus, however, there is Fig. 233.

herent to it. 3, 4, 5. Circular muscular fibres in different parts of the intestine.

Fig. 234.

a minute vascular plexus, the larger branches of which, when distended with blood, may be seen even by the naked eye. Marginal illustration, Fig. 235, exhibits the vessels of one of the intestinal villi of the hare, from Wagner, after an extremely beautiful dry preparation by Döllinger, magnified about 45 diameters. The most obvious use of these villi is to increase the surface from which the secretion is prepared, and from which absorption is effected. Within the membrane

'J. Müller, Elements of Physiology, by Baly, 2d edit., p. 285, Lond., 1840.

are numerous follicles, which, with the exhalants, secrete a mucous fluid, called by Haller succus intestinalis. Their entire number in the whole alimentary canal is estimated by Dr. Horner to be 46,900,000. At about four or five fingers' breadth from the pylorus, the duodenum is perforated by the termination of the biliary and pancreatic ducts, which pour bile and pancreatic fluids into it. (Fig. 219.) Generally, these ducts enter the intestine by one opening; at times, they are distinct, and lie alongside each

Fig. 235.

Hare.

1, 1. Veins filled with white

other. The structure of Bloodvessels of Villi of the
the duodenum is the same
as that of the whole of
the intestinal canal. The
muscular coat is, however,

injection. 2, 2. Arteries filled
with red. A beautiful rete of
capillaries between the two.

thicker, and the peritoneal coat only covers its first portion, passes before the second, and is totally wanting in the third, which we have described as included in the transverse mesocolon.

Fig. 237.

The other two portions of the small intestine are of considerable length; the jejunum commencing at the duodenum, and the ileum terminating, in the right iliac fossa, in the first of the great intestines-the cæcum. They occupy the middle and almost the whole of the abdomen, being surrounded by the great intestine (Fig. 210). The jejunum is so called from being generally found empty; and the ileum from its numerous windings. The line of demarcation, however, between the duodenum and jejunum, as well as between the latter and the ileum, is not fixed: it is an arbitrary division. The jejunum has, internally, the greatest number of valvula conniventes and villi. The ileum is the lowest portion. It is of a paler colour, and has fewer valvula conniventes. jejunum is situate at the upper part of the umbilical region; the ileum at the lower part, extending as far as the hypogastric and iliac regions. The mucous membrane of the jejunum and ileum resembles, in all essential respects, that of the duodenum; the valvulæ conniventes are,

2

The

One of the Glandula
Majores Simplices of

the Large Intestine,
as seen from above,
and also in a Section.

Special Anatomy and Histology, 7th edit., ii. 55, Philad., 1846.

however, more numerous in the jejunum than in the duodenum; and, in the course of the ileum, they gradually disappear, and are replaced by simple longitudinal ruge. The villi, too, which are chiefly destined for chylous absorption, abound in the jejunum, but gradually disappear in the ileum. The mucous membrane of both is largely supplied with follicles, called glands of Peyer, Brunner, and Lieberkühn; some, if not all, of which are probably concerned in secreting the succus entericus, succus intestinalis,-a mucous fluid, to which in digestion Haller attached unnecessary importance. M. Lelut' estimates the number of these glands in the small intestine at 40,000. Dr. Horner considers. the follicles to be formed, in every instance, of meshes of veins; the arteries entering inconsiderably into their composition,-in about the same proportion as they do in other erectile tissues.2

The glands, as they are termed, of the small intestine have long been known under the name of follicles of Lieberkühn. These become especially evident if the mucous membrane is inflamed, when they are filled with an opaque whitish secretion, which is absent in the healthy state.

Fig. 239.

The true glands of Brunn or Brunner are chiefly in the duodenum. They are situate in the submucous tissue, where they form a continuous layer of white bodies surrounding the intestine. They are not larger than a hemp-seed; each consisting of numerous minute lobules, the ducts of which open into a common excretory duct. They are complex structures, differing from the other glands and follicles of the intestines. Nothing is positively known of the nature of their secretion. The glands of Peyer form large patches on the mucous membrane, when they are called glandulae agminate and Peyer's patches. Examined in a healthy mucous membrane, they have the appearance of circular white, slightly raised spots, about a line in diameter, over which the mucous membrane is least studded with villi, and often wholly without them. On rupturing one of the white bodies a cavity is found, but it has no excretory duct. It contains a grayish-white mucous matter. There are likewise closed solitary glands in both the small and *large intestines. The precise use of the glands of Peyer is unknown. Wagner' has well observed, that the intimate structure of the whole of these glandular bodies requires farther study, and is almost as little known as their individual functions. There is reason to believe, however, that they secrete a putrescent matter from the blood, which may be concerned in giving to the excrement its peculiar odour; this matter, as in other cases, being formed by cells, which

Conglomerate Gland of Brunner, magnified 100 times. (Boehm.)

1 Gazette Médicale, Juin, 1832. 2 Op. cit., ii. 54.

3 Boehm, cited in Brit. and For. Med. Rev., i. 521, Lond., 1836. 4 Baly, Lond. Med. Gazette, Mar., 1847.

6 Elements of Physiology, translated by R. Willis, § 137, Lond., 1812.

burst on the free surface of the mucous membrane, and discharge their contents to be mixed with the fæces. The marginal figure, after Bendz,' illustrates the morphology of a Peyer's gland.

The muscular coat of the small intestine is composed of circular and longitudinal fibres; and the outer coat is formed by the prolongation of the peritoneum, which, after having surrounded the intestines, completes the mesentery, by which the gut floats, as it were, in the abdominal cavity.

Fig. 242.

d

side View of Intestinal Mucous Membrane of a Cat. (After Bendz.)

a. A Peyer's gland, imbedded in submucous tissue, f. b. A tubular follicle. c. Fossa in mucous membrane. d. Villi. e. Follicles of Lieberkühn.

The large intestine terminates the intestinal canal. It is much shorter than the small, and considerably more capacious, being manifestly intended, in part, as a reservoir. It is less loose in the abdominal cavity than the portion of the tube which we have described. It commences at the right iliac fossa (Fig. 210, 9); ascends along the right flank, as far as the under surface of the liver; crosses over the abdomen to gain the left flank, along which it descends into the left iliac region, and

1 Haandbog i den Almindenige Anatomie, Kjöbenhavn, 1847, cited by Kirkes and Paget, Manual of Physiology, Amer. edit., p. 186, Philad., 1849.