912 THE ORGANS OF DIGESTION. 



termination. It is contained in the central and lower part of the abdominal cavity, 

 and is surrounded above and at the sides by the large intestine ; a portion of it 

 extends below the brim of the pelvis and lies in front of the rectum ; it is in relation, 

 in front, with the great omentum and abdominal parietes ; and connected to the 

 spine by a fold of peritoneum, the mesentery. The small intestine is divisible into 

 three portions the duodenum, the jejunum, and ilium. 



The duodenum has received its name from being about equal in length to the 

 breadth of twelve fingers (ten inches). It is the shortest, the widest, and the most 

 fixed part of the small intestine. Its course presents a remarkable curve, which 

 in the adult, as regards the greater part of its extent, is U-shaped ; though some- 

 times, in consequence of the transverse portion being very short or altogether 

 wanting, it partakes more of the character of the letter V. In children, up to the 

 age of about seven, the duodenum is annular ; its two extremities are on about the 

 same level ; and between them it describes a regular curve embracing the head of 

 the pancreas, the neck of which lies between the two extremities of the ring. 



In the adult the course of the duodenum is as follows : commencing at the 

 pylorus the direction of the first portion depends upon the amount of distention 

 of the stomach and therefore upon the position of the pylorus. When the stomach 

 is empty and the pylorus situated at the right of the upper border of the first 

 lumbar vertebra, it is nearly horizontal and transverse ; but where the stomach is 

 distended, in consequence of the alteration of the position of the pylorus to the 

 right the proximal end of the duodenum also becomes altered in position, while the 

 distal end remains fixed and the direction of this portion of the bowel is now antero- 

 posterior. Whether directed transversely or antero-posteriorly, it reaches the 

 under surface of the liver, where it takes a sharp curve and descends along the 

 right side of the vertebral column, for a variable distance, generally to the body of 

 the fourth lumbar vertebra. It now takes a second bend, and passes across the 

 front of the vertebral column from right to left and finally ascends on the left side 

 of the vertebral column and aorta to the level of the upper border of the second 

 lumbar vertebra and there terminates in the jejunum. As it unites with the 

 jejunum it often turns abruptly forward, forming the duodeno-jejunal angle. From 

 the above description it will be seen that the duodenum may be divided for purposes 

 of description into four portions superior, descending, transverse, and ascending. 



The first or superior portion (Fig. 496) is very variable in length, but is usually 

 estimated as being about two inches. Beginning at the pylorus, it ends at the 

 neck of the gall-bladder. It is the most movable of the four portions. It is 

 almost completely covered by peritoneum derived from the two layers of the lesser 

 omentum, but a small part of its posterior surface near the neck of the gall-bladder 

 and the inferior vena cava is uncovered. It is in such close relation with the gall- 

 bladder that it is usually found to be stained by bile after death, especially on its 

 anterior surface. It is in relation above and in front with the quadrate lobe of the 

 liver and the gall-bladder; behind with the gastro-duodenal artery, the common 

 bile-duct, aud the vena porta ; and below with the head of the pancreas. 



The second or descending portion is between three and four inches in length, 

 and extends from the neck of the gall-bladder on a level with the first lumbar 

 vertebra along the right side of the vertebral column as low as the body of the 

 fourth lumbar vertebra. It is crossed in its middle third by the transverse colon, 

 the posterior surface of which is uncovered by peritoneum and is connected to the 

 duodenum by a small quantity of connective tissue (Fig. 490). The portions of the 

 descending part of the duodenum above and below this interspace are named the 

 supra- and infra-colic portions, and are covered in front by peritoneum. The right 

 side of the supra-colic portion is covered by peritoneum derived from the anterior 

 surface of the right kidney, the left side of the same portion being covered by the 

 peritoneum forming the lesser sac. The infra-colic part is covered by the right 

 leaf of the mesentery. Posteriorly the descending portion of the duodenum is 

 uncovered by peritoneum. It is in relation, in front, with the transverse colon, 

 and above this with the liver ; behind with the front of the right kidney, to which 





