1022 THE DIGESTIVE SYSTEM. 
ment to the intestinal wall, it will be seen that its free edge is not only undulating, but is frilled or 
plaited to an extreme degree. When shown in this way, it is found that the plaiting or folding 
is not quite indiscriminate, but that the main folds, of which there are usually six, run alter- 
nately to the right and left. Asa rule, the first fold runs to the left from the duodeno-j jejunal 
flexure, and goes to a coil of jejunum whic h lies under the transverse mesocolon, and he Ips to 
support the stomach (this coil has been already referred to, page 1003). The second fold passes 
to the right, the third to the left, and so on up to the fifth and sixth, which are usually small. 
From the margins of these primary folds secondary folds project in all directions, and from these 
again even a third series may be formed. 
~ This order is of course by no means constant, but if the intestine be removed from a hardened 
body in the way suggested, ‘without disturbing the mesentery, it will be found to be arranged 
with more or less regularity on some such plan as that indicated. 
Arrangement of Coils of Small Intestine.— Although the greatest variety is 
found in the disposition of the small intestine, and it is impossible to state im what 
recions of the abdomen the different parts of the tube will be found, still it may 
be said that in general the jejunum (as might be expected from the position at 
which it begins) is placed above and to the left, in reference to the ileum, which 
latter hes below and to the right. Again, the upper part of the jejunum is usually 
situated to the left of the duodeno-jejunal flexure, in contact with the under 
surface of the pancreas and transverse mesocolon ; and, similarly, the terminal part 
of the ileum almost always lies in the pelvis, from which it passes up over the 
right side of the pelvic brim to reach the ileo-cecal orifice. Another portion 
of the small intestine is not uncommonly found in the pelvis; this is the part 
with the longest mesentery, and lies between two points, six and eleven feet 
respectively from the duodenum (Treves). 
Differences between Jejunum and Ileum.—If the small intestine be followed 
down from the duodenum to the cecum no noticeable change in appearance will 
be found at any one part of its course, to indicate the transition from jejunum to 
ileum ; for the one passes insensibly into the other. Nevertheless, a gradual change 
takes place, and if typical parts of the two, namely, the upper portion of the 
jejunum and the lower portion of the ileum, be examined, they will be found 
to present characteristic differences, which are set forth in the following table :— 
| | | 
J pee | Tleum. | 
E a : io, eee oe 1 eee 
Wider, 13 to 14 inch in diameter. Narrower, 14 to 1 inch in diameter. | 
Wall, thicker and heavier. Wall, thinner and lighter. | 
2edder and more vascular. Paler and less vascular. 
Valvule conniventes well developed. | Valvulze conniventes absent or very small. 
Peyer’s patches, few and small. | Peyer’s patches, large and numerous. | 
The villi are also said to be shorter and broader in the jejunum, more slender 
and filiform in the ileum (Rauber). 
The terminal portion of the ileum, after crossing the brim of the pelvis, runs 
upwards, and also slightly backwards and to the right, in close contact with the 
evcum, until the ileo-ceecal orifice 1s reached. 
Meckel’s Diverticulum (diverticulum ilei)—This is a short wide protrusion which is found 
springing from the lower part of the ileum in a little over 2 per cent of the bodies examined. 
It is usually about 2 inches long, and of the same width as the intestine from which it 
comes off. Most commonly it is found about 23 feet from the ileo-ceecal valve, and opposite 
the termination of the superior mesenteric artery. As a rule, it runs at right angles to 
the gut, and its end is free; but occasionally it is adherent either to the abdominal wall, 
the adjacent viscera, or the mesentery, when it may be the cause of strangulation of the 
intestine. 
The diverticulum is due to the persistence of the proximal portion of the vitelline (or vitello- 
intestinal) duct, which connects the primitive intestine of the embryo with the yolk sae. In 
shape it may be cylindrical, conical, or cord-like, and it may present secondary diverticula near 
its tip. It arises most frequently from the free border of the intestine, but it sometimes comes 
off from the side. It runs at right angles to the gut most commonly, but it may assume any 
direction, and it often is prov ided with a mesentery. In 3302 bodies specially examined with 
reference to its existence, it was present in 73, or 2°2 per cent, and it appeared to be more common 
in the male than in the female. In 59 out of the 73 cases its position with reference ke ithe end 
of the ileum was examined: its average distance from the ileo-ceecal valve was 325 inches 
