1208 THE DIGESTIVE SYSTEM. 



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 joancreatico-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 cceliac glands ; some also 

 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 cceliac glands. 



The nerves, which are almost entirely non-medullated, come from the plexus cceliacus, 

 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 caecum 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; (&) the mesenteric lymph glands, 

 which vary from 40 to 150 in number; (c) a considerable amount of fatty con- 

 nective 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 meso- 

 colon. 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 



