THE DUODENUM. 1015 
THE DUODENUM. - 
The duodenum, the portion of the digestive tube which immediately succeeds 
the stomach, is the first part of the small intestine, and differs from the rest of 
that tube in having no mesentery, and also in being closely fixed to the posterior 
abdominal wall—conditions which are evidently associated with its relation to the 
bile and pancreatic ducts, both of which open into its cavity. 
Shape and Divisions.—The duodenum begins at the pylorus, about the level 
of the first lumbar vertebra, and ends, after a somewhat C-shaped course, at the 
left side of the first or second lumbar vertebra (Fig. 687). It is generally described 
as being ade up of three parts, namely :—(1) The first or superior portion which 
begins at the pylorus, passes backwards and to the right beneath the liver, and 
ends at the neck of the gall-bladder, by turning down and joining (2) the second 
or descending portion. This begins at the neck of the gall-bladder, runs down 
behind the transverse colon (Fig. 688), and ends opposite the third or fourth 
lumbar vertebra by turning to the left, and passing into (3) the third or inferior 
portion. This at first runs more or less transversely to the left, across the vena 
cava, and then ascends, in front of the aorta, as far as the under surface of the 
pancreas, where, at the level of the first or second lumbar vertebra, it bends 
abruptly forwards, forming the duodeno-jejunal flexure (Fig. 687), and passes into 
the jejanuin. 
Taking the whole of the duodenum together, it forms an irregularly C-shaped 
curve, with the opening of the C directed upwards and to the left, and the 
ends reaching to within about two inches of one another. Within the concavity 
of the curve the head of the pancreas is placed. 
The incomplete ring which the duodenum makes does not all lie in the same 
plane; for, whilst its greater part is placed in a transverse-vertical plane, the 
middle portion bends strongly backwards, round the right side of the vena cava, 
and lies almost in a sagittal plane (Fig. 687). 
Position and Size.—As a rule, a little more than half of the duodenum lies 
in the epigastrium, the remainder, namely, about the lower third of the descending 
portion and the adjoining two-thirds of the inferior or third portion, are placed in 
the umbilical region. With the exception of the terminal ascending portion of the 
third part, the whole of the duodenum les to the right of the middle line. 
Its length is usually about 11 inches (27:5 em.), its first portion being the shortest 
and its third portion the longest. Its diameter varies considerably, and may be 
stated to average about 1} inches when empty, but it may be as much as two 
inches when distended. 
Relations.—The first or superior portion (pars superior) begins at the pylorus 
opposite the first lumbar vertebra. From this it runs to the right, and then 
backwards, beneath the liver, when the stomach is empty; but directly backwards 
when it is full; and ends at the neck of the gall-bladder by turning downwards 
and passing into the second part. Its length varies from about 1} to 2 inches 
(3°7 to 5-0 em.), and is said to be greater when the stomach is empty than when 
distended. 
Its relations (Figs. 687 and 688) are as follows :—<Above and in front lies the 
quadrate lobe of the liver, which hangs downwards and to the right over the tube. 
Below, it rests on the head and neck of the pancreas (the latter running up behind 
it for a little way). Behind it, close to the pylorus, the portal vein ascends to the 
liver, and the bile duct with the gastro-duodenal artery passes downwards. Further 
to the right, as it bends backwards, it hes against the right side of the vena cava. 
Its peritoneal relations for about an inch from the pylorus are the same as those 
of the pyloric end of the stomach, that is to say, both the anterior and posterior 
surfaces are covered, and the lesser and great omenta are attached to its upper 
and lower borders respectively (Fig. 688). Beyond this, however, only the anterior 
surface has a serous coat. 
The peritoneal covering of the first half of the posterior surface is derived from a diver- 
ticulum of the small sac which runs to the right behind the duodenum for the distance, 
mentioned. 
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