107 THE DIGESTIVE SYSTEM. 
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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 Brunner’s glands; otherwise it corresponds very closely to 
a serous salivary gland, the general strueture of which will be found on page 958. 
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 (page 1020), ought perhaps to be mentioned in 
this connection. 
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. 723), sending 
branches outwards 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; 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. (38) The inferior pancreatic branch of the superior mesenteric (or sometimes of the gastro- 
duodenal) artery, a considerable branch, which arises along with, or near, the last, and runs to the 
left along the lower border of the pancreas, often even as far as its-tail. (4) Pancreatic branches 
of the splenic artery, are several (3 to 5) fair-sized branches which come off from the splenic 
as it runs behind the upper 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. (5) Small pancreatic branches also arise from the hepatic 
artery whilst it rests on the upper part of the gland, and enter it immediately. The pan- 
creatica magna, which is described as accompanying the duct from left to right, does not seem 
to exist in the majority of cases. 
The veins are: (1) An anterior pancreatico-duodenal (Fig. 723), which passes downwards and 
to the left, on the front of the head, and joins the superior mesenteric ; (2) a posterior pancreatico- 
duodenal, which crosses the back of the head, and opens into the portal vein; (3) several small 
pancreatic veins which join the splenic; and (4) some from the upper part of the head and 
neck join the portal, which latter vein ultimately receives all the blood returned from the 
gland. 
The lymphatics pass chiefly with the splenic lymphatics to the coeliac glands; some also are 
connected with a few glands which lie near the upper end of the superior mesenteric vessels. Al] 
the lymphatics of the organ pass ultimately to the ceeliae glands. 
The nerves, which are almost entirely non-medullated, come from the solar plexus, through 
the coeliac, splenic, and superior mesenteric plexuses. 
DEVELOPMENT OF THE PANCREAS. 
The pancreas is developed at a very early period in man (being visible in embryos of 
8 mm.) from at least two independent hollow outgrowths, one of which takes place from the 
ventral aspect of the future duodenum in connection with the diverticula which form the 
liver; the other from the dorsal side of the tube. From this latter, which springs from the 
duodenum nearer to the pylorus than the ventral outgrowth, the greater part of the gland 
is formed, whilst the ventral diverticulum gives rise to the smaller portion. About the 
sixth week the two outgrowths meet, and they, as well as their ducts, fuse. At first the 
main duct of the gland is connected with the dorsal outgrowth ; later on, the portion of 
this duct between the duodenum and the meeting of the two ducts lags behind in its 
growth, whilst the corresponding portion of the ventral duct increases rapidly in size ; and 
finally, this latter appears to be the direct continuation of the main duct, whilst the 
former, and now much smaller, dorsal duct, becomes the accessory pancreatic duct. The 
two ducts come to open on the inner or left side of the gut, owing to the turning over of 
the duodenum on its right side, and the unequal growth of different portions of its wall. 
The primary diverticula give off hollow lateral buds, which in their turn give off 
others, and this process is continued until the mass of the gland is formed. The terminal 
buds thus produced develop into the gland acini, whilst the others form the gland ducts. | 
When first formed in the embryo, the pancreas runs upwards towards the head, behind 
the stomach-and between the two layers of the mesogastrium, so that it possesses a 
complete peritoneal covering. Subsequently, as a result of the changes which take place 
in the position of the stomach, it turns over on to its right side, and becomes adherent to 
the posterior abdominal wall, its head occupying the concavity of the duodenum, and its 
tail passing towards the spleen. The peritoneum of its posterior surface is soon lost by . 
absorption ; but it persists on its anterior aspect. 
