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in its right half, it is continuous with the neck; whilst to the left of this it is separated from the neck by a deep notch, incisura pancreatis, in which lie the superior mesenteric vessels (Fig. 946). Its right and inferior borders are moulded on to the side of the duodenum, which lies in a groove of the gland substance the bile-duct being interposed as far down as the middle of the descending part of the duodenum. The posterior surface of the head is applied to the front of the vena cava inferior; it also lies on the right renal vessels and the left renal vein, and, at its left end, on the aorta as well. Its anterior surface is in contact above and on the right with the beginning of the
FIG. 947. THE PERITONEAL RELATIONS OF THE DUODENUM, PANCREAS, SPLEEN, KIDNEYS, ETC.
transverse colon (Fig. 947), without the interposition of the peritoneum as a rule. this it is clothed by peritoneum, and is covered by the small intestine.
The superior mesenteric vessels, after passing forward through the pancreatic notch, descend in front of that portion of the head (processus uncinatus) which runs to the left along the third part of the duodenum. The superior pancreatico-duodenal vessels run downwards, and break up on the front of the head (Fig. 946).
The neck (Fig. 946) is a comparatively attenuated portion of the gland which lies in front of the portal vein, and connects the head to the body. Springing from the upper portion of the head, it runs forwards, upwards, and to the left for about 1 inch (25 mm.), and then passes into the body.
The neck is about inch (18 mm.) in width, and less than inch (12.5 mm.) in thickness. In front and to its right lie the first part of the duodenum and the pylorus; behind and to the left it rests upon the beginning of the portal vein, which is formed under cover of its lower border by the union of the splenic and superior mesenteric veins. It has a partial covering of peritoneum on its anterior surface; and its beginning is generally marked off from the head by the gastro-duodenal artery, with its continuation the superior pancreatico-duodenal, which lies in a groove of the gland substance between the head and neck.
Corpus Pancreatis.-The body is of a prismatic form, largest where it lies in front of the left kidney, and usually somewhat tapering towards the tail (Fig. 948 Beginning at the termination of the neck, it runs backwards and to the left across the front of the left kidney, beyond which its extremity or tail comes in contact with the spleen. When hardened in situ it presents three surfaces-anterior, inferior, and posterior-all of which are of nearly equal width (namely, about 14 inches: 31 mm.).
Facies Anterior. The anterior surface is widest towards the left end; it looks upwards and forwards (Fig. 947), and forms a considerable portion of the stomach-bed. This surface is completely covered by peritoneum, derived from the posterior wall of the bursa omentalis, which latter separates the pancreas from the posterior surface of the stomach. Towards its right extremity it usually presents an elevation or prominence where the body joins the neck. This projects against the back of the lesser omentum when the stomach is distended, and is consequently known as the tuber omentale.
Facies Inferior.-The inferior surface, which, like the anterior, is, as a rule, widest towards its left eud, looks downwards and slightly forwards. It is completely covered by peritoneum, continuous with that forming the posterior layer of the transverse mesocolon (Fig. 947). It lies in contact with the duodeno-jejunal flexure towards its right end, with the left flexure of the colon near its left end, and with a mass of small intestine (jejunum, which is always found packed in beneath it) in the rest of its extent.
Facies Posterior. The posterior surface looks directly backwards, and is entirely destitute of peritoneum. It is connected by areolar tissue to the posterior abdominal wall with the organs lying upon it. From right to left these are: the aorta with the origin of the superior mesenteric artery, the left renal vessels, the left supra-renal gland, and the left kidney. In addition, the splenic artery runs its tortuous course to the left along the superior border of the pancreas, whilst the splenic vein runs, behind the gland, at a lower level than the artery.
The three surfaces of the body of the pancreas are separated by three borders. The margo anterior is the most prominent, and gives attachment to the transverse mesocolon (Fig. 947). It is, as it were, squeezed forward, by the pressure of the stomach above and the small intestine below, into the interval between these two sets of viscera, thus following the line of least resistance (Cunningham). Towards the neck this border is no longer prominent, but becomes rounded off, so that here the superior and inferior surfaces are confluent.
The coeliac artery projects over the margo superior, and sends its hepatic branch to the right, resting upon it, whilst the splenic artery runs to the left along it (Fig. 947). The margo inferior calls for no special description.
Cauda Pancreatis.—The tail of the pancreas is the somewhat pointed left end of the body, which is in contact with the inferior portion of the gastric surface of the spleen It usually presents an abrupt, blunt ending, in which case it is related to the spleen in the manner just described; or it may be elongated and narrow, when it bends backwards around the lateral aspect of the kidney, and beneath the base of the spleen. In either case it is in near relation below with the left flexure of the colon (Fig. 947).
Peritoneal Relations of the Pancreas.-The posterior surface of the pancreas is entirely free from peritoneum. The other surfaces derive their peritoneal covering from the prolongation of the two layers of the transverse mesocolon, which is attached to the anterior border of the gland, from the tail to the neck. At this border the two layers separate (Fig. 914, p. 1160), the anterior-derived from the bursa omentalispassing backwards and upwards over the anterior surface; the posterior-derived from the large sac-turning downwards and backwards along the inferior surface.
As the transverse mesocolon is followed to the right it is, as a rule, found to terminate near the neck of the pancreas (Fig. 947). Beyond this, the posterior surface of the colon is generally free from peritoneum, and is connected by areolar tissue to the anterior aspect of the head of the gland. Below the level of the colon the head is covered by the continuation downwards of the peritoneum from the inferior surface of that gut. Often, however, the transverse mesocolon is continued to the right as far as the right colic flexure, and the anterior surface of the head then completely covered by peritoneum.
Ducts of the Pancreas.-Almost invariably two ducts are found in the interio? of the pancreas-the ductus pancreaticus [Wirsungi] or pancreatic duct proper and the ductus pancreaticus accessorius [Santorini], accessory pancreatic duct (O.T. duct of Santorini).
The pancreatic duct [Wirsungi] begins near the tip of the tail by the union of small ducts from the lobules forming that part of the organ. From there it pursues
a rather sinuous or zigzag course (Fig. 948) through the axis of the gland, at first running transversely to the right, until the neck is reached, then it bends downwards into the head, approaches the descending part of the duodenum, and meets the bile-duct. The two ducts pierce the medial wall of the gut obliquely (for to of an inch, 12 to 18 mm.), and open, by a common orifice on the duodenal papilla, about 3 or 4 inches (8.7 to 10 cm.) beyond the pylorus (see p. 1203).
In its course through the gland the pancreatic duct receives numerous tributaries, which join it, as a rule, nearly at a right angle. The tributaries, as well as the main duct itself, are easily recognised by the whiteness of their walls, which contrasts with the darker colour of the gland tissue. The main duct receives tributaries from all portions of the pancreas, and towards its termination attains a considerable size (namely, th to 4th of an inch-2.5 to 4 mm.-when flattened out, or somewhat larger than a crow quill).
Superior part of duodenum
FIG. 948.-POSTERIOR ASPECT OF THE PANCREAS AND DUODENUM, with the pancreatic duct exposed. The superior mesenteric vessels also are shown in section, passing forwards, surrounded by the recurved portion of the head of the pancreas.
The pancreatic accessory duct (O.T. duct of Santorini) is a small and variably developed duct (Fig. 948) which opens into the duodenum about of an inch above and somewhat anterior to the pancreatic duct. From the duodenum it runs to the left and downwards, and soon divides into two or more branches, one of which joins the pancreatic duct, the others pass down and receive tributaries from the lower part of the head. It is generally supposed that the current flows from this into the main duct, and not into the duodenum, as a rule, except in early life.
Physical Characters and Structure of the Pancreas. The pancreas is of a reddish cream colour, soft to the touch, and distinctly lobulated. The lobules are but loosely held together by their small ducts and by loose areolar tissue; for, as already pointed out, the pancreas is devoid of a regular capsule, and possesses instead merely an adventitious coat of fine connective tissue.
The gland belongs to the class of acino-tubular glands, its alveoli or acini being elongated like those of the duodenal glands; otherwise it corresponds very closely to a serous salivary gland, the general structure of which will be found on p. 1140. The secretion is termed succus pancreaticus.
Variations. The chief variations found are:-(1) A separation of the part of the head, known as the uncinate process, which then forms a lesser pancreas. (2) A growth of the pancreas around the duodenum, which it may practically encircle for a short part of its course. And (3) an opening of its duct into the duodenum, independently of the bile-duct. An accessory pancreas (pancreas accessorium) is also sometimes found in the wall of the stomach or of the jejunum. Diverticula of the duodenum, already described (p. 1187), ought perhaps to be mentioned in
Vessels. The arteries of the pancreas are:-(1) The superior pancreatico-duodenal, a branch of the gastro-duodenal artery, which runs down on the front of the head (Fig. 946), sending branches laterally to the duodenum, as well as numerous twigs into the substance of the pancreas. (2) The inferior pancreatico-duodenal, a branch of the upper part of the superior mesenteric artery; or from the root of one of the rami jejunales; it runs upwards and to the right across the back of the head, and sends branches to it and to the duodenum, one of which runs between the head and the duodenum. These two pancreatico-duodenal arteries anastomose around the inferior border of the head. (3) Pancreatic rami from the splenic artery, are several (3 to 5) fair-sized branches
which come off from the splenic as it runs behind the superior border of the gland; they enter the pancreas immediately, and traverse its substance from above downwards, some sending branches in both directions along the course of the pancreatic duct.
The veins are: (1) The pancreatico-duodenal veins (Fig. 947), of which some pass downwards and to the left, on the front of the head, and join the superior mesenteric; while others cross the back of the head, and open into the superior mesenteric; (2) several small pancreatic veins which join the splenic.
The lymph vessels pass chiefly with the splenic lymph vessels to the coeliac glands; some also a are connected with a few glands which lie near the upper end of the superior mesenteric vessels. All the lymph of the organ passes ultimately to the cœliac glands.
The nerves, which are almost entirely non-medullated, come from the plexus cœliacus, through the hepatic and splenic plexuses.
INTESTINUM TENUE MESENTERIALE.
INTESTINUM JEJUNUM AND INTESTINUM ILEUM.
The upper two-fifths, that is, about 8 feet, of the small intestine beyond the duodenum, are known as the intestinum jejunum. The succeeding three-fifths, which usually measure about 12 feet, constitute the intestinum ileum. The ileum opens into the large intestine at the junction of the cæcum and ascending colon, where its orifice is guarded by the valvula coli.
Both the jejunum and ileum are connected to the parietes by a large fold of peritoneum the mesentery-which conveys vessels and nerves from the posterior abdominal wall to these divisions of the intestine.
The part of the tube to which the mesentery is connected is known as the mesenteric or attached border; the opposite side is the free border.
Mesenterium. The mesentery is a broad fan-shaped fold, composed of two layers of peritoneum, which connects the small intestine to the posterior wall of the abdomen. The long free border of the fold contains the intestine within it (Fig. 949) The other, or attached border, known as the radix mesenterii (root of the mesentery), is comparatively short, being only 6 or 7 inches long; but it is much thicker than the part near the gut, for it contains between its layers a considerable amount of fatty extra-peritoneal tissue, in addition to the large vascular trunks passing to the intestine. The root is attached to the posterior abdominal wall along an oblique line, extending approximately from the left side of the second lumbar vertebra to the right iliac fossa (Fig. 949). In this course its line of attachment passes from the duodeno-jejunal flexure down over the front of the terminal part of the duodenum, then obliquely across the aorta, the inferior vena cava, the right ureter, and psoas major muscle, to reach the right iliac region.
The unattached border of the mesentery is frilled out to an enormous degree, so that, while the root measures but 6 or 7 inches, the free border is extended to some 20 feet, thus resembling a fan, one border of which may be twenty or thirty times as long as the other. The length of the mesentery, measured from its root to the attached edge of the intestine directly opposite, usually measures at its longest part about 6 inches (8 or 9 inches, Treves and Lockwood).
Between the two layers of the mesentery (Fig. 928) are contained (a) the jejunal and ileal branches of the superior mesenteric vessels, accompanied by the mesenteric nerve plexus and lymph vessels; (b) the mesenteric lymph glands, which vary from 40 to 150 in number; (c) considerable amount of fatty connective tissue, continuous with the extra-peritoneal areolar tissue; and (d) the intestine itself.
The peritoneum from the right side of the mesentery passes out on the posterior abdominal wall to clothe the ascending colon, and, above, it is connected by a fold with the transverse mesocolon. That of the left side, similarly, passes across the parietes to the descending and iliac portions of the colon.
The mesentery begins above, immediately beyond the ending of the duodenum-that is, in the angle of the duodeno-jejunal flexure-and it ends below in the angle between the ileum and ascending colon. It is very short at each end, but soon attains the average length. Its longest part goes to the portion of the small intestine situated between two points, one six feet, the other eleven feet from the duodenum (Treves).
Whilst the root of the mesentery pursues at its attachment an almost straight line from one end
to the other, if cut across a very short distance from the posterior abdominal wall, it will here be found to form a wavy or undulating line. Further away still this condition becomes more and more marked; and finally, if the bowel is removed by cutting through the mesentery close to its attachment to the intestinal wall, it will be seen that its free edge is not only undulating, but is frilled or plaited to an extreme degree. When shown in this way, it is found that the plaiting or folding is not quite indiscriminate, but that the main folds, of which there are usually six, run alternately to the right and left. As a rule, the first fold runs to the left from the duodeno-jejunal flexure, and goes to a coil of jejunum which lies under the transverse mesocolon, and helps to support the stomach. The second fold passes to the right, the third to the left, and so on up to the fifth and sixth, which are usually small. From the margins of these primary folds secondary folds project in all directions, and from these again even a third series may be formed.
This order is of course by no means constant, but if the intestine is removed from a hardened body in the way suggested, without disturbing the mesentery, it will be found to be arranged with more or less regularity, on some such plan as that indicated.
Differences between Jejunum and Ileum.-If the small intestine is followed down from the duodenum to the cæcum no noticeable change in appearance will be found at any one part of its course, to indicate the transition from jejunum to ileum; for the one passes insensibly into the other. Nevertheless, a gradual change takes place, and if typical parts of the two, namely, the upper portion of the jejunum and the lower portion of the ileum, is examined, they will be found to present characteristic differences, which are set forth in the following table:
Wider, 1 to 1 inch in diameter.
Redder and more vascular.
Narrower, 1 to 1 inch in diameter.
Paler and less vascular.
Plicæ circulares, absent or very small.