THE SMALL INTESTINE 



965 



in (liaiuctcr, and is al)()ut ten inches lon-r. Tt lias been compared in general sliajjc 

 to a liorsc'shoc, though not very aptly, as the one side is so much hjiiger than the 

 other. It is arranged in a curved manner round the pancreas, and readily lends 

 itself to a division into four parts (tig. 577). 



Tlie Jird part — the superior, or a>icendin(j — is hardly t\V(j inches long. Begin- 

 ning at tlie ])yl()rus, and passing upwards and backwards to the right, it ends at the 

 neck of the gall-bladder. It is the most moval)le of tlie four portions. It is 

 covered l)y the two layers of peritoneum which are continued from the stomach, and 

 by these it is completely surrounded in front, but is only covered behind in the 

 vicinity of the pylorus. Above it are found the liver (quadrate lobe) and gall 

 l)ladder. The gut itself forms the lower boundary of the foramen of Winslow. 

 Below it is the pancreas; and behind are the common bile-duct, hepatic vessels and 

 portal vein. 



The second jxirt — the descendiiuj portion — not (luite three inches long, extends 

 from the neck of the gall l)ladder t(j the third lumljar vertebra, a short bend mark- 

 ing the separation between the first and second ])arts. This part is covered In- peri- 

 toneum in front only, the memljrane l)eing derived from a continuation of the 

 •superior layer of the transverse meso-colon (fig. 570). 



Fig. 570. — The Duodenum from ik front. 



superior layer of transverse meso-colon 



SECOND PART OF 

 DUODENUM 



FOURTH PART OF DUODENUM 



INFERIOR LAYER OF TRANSVERSE MESO-COLON 



THIRD PART OF DUODENUM 



SUPERIOR MESENTERIC VESSELS 



It is more fixed than the first portion. It is in relation in front with the trans- 

 verse colon and meso-colon. On its leftside is the pancreas (fig. 577), and the 

 common l)ile-duct a little more i)osteriorly. The looj) formed by the pancreatico- 

 duodenal arteries runs also along the left margin of this part of the bowel. 



Behind lie tlie right kidney and the renal vessels and vena cava (fig. 590). 



Some of the nmscular fibres of this part of the duodenum are said to be continu- 

 ous with the lobules of the pancreas. Into this segment of the bowel, at its inner 

 and back part and some four inches from the ]\vlorus tlie common bile-duct and 

 pancreatic duct enter (figs. 571, 58(5, and 587). 



The tJiird part, or tranxrcrxe portion, is the longest, l)eing al)out five inches long. 

 It extends from the body of the third luml)nr vertebra on the right side, and ]>asses 

 ol)li(]uely across the spine to the ujijier ])art of the left side, ascending a little on 

 its way. In front of the third part of the duo<lenum is found the lower layer of 

 the transverse meso-colon. The su])crior mesenteric vessels cross this part of the 

 bowel, running lietween it and the pancreas to reach the mesentery (fig. 570). 

 Along the ujiper Ijorder runs the inferior pancreatico-duodenal artery. The gut is 

 in relation above with the pancreas and su]ierior mesenteric artery. Behind are 

 the vena cava, aorta, and crura of the dia|)hragm (figs. 571, 577). It is the most 

 fixed portion of the duodenum, and is covered in front only by |)eritoneum. 



