1656 HUMAN ANATOMY. 



ileum when its mesentery has been elongated by prolonged stretching, as in the 

 presence of an old hernia (Maylard); {e) internal hernice, as into the duodeno- 

 jejunal, pericaecal, or intersigmoid fossae, or through the foramen of Winslow, or 

 through an aperture in the omentum (page 1758), which may be traumatic or may 

 be one of the rounded openings due to congenital atrophy of a comparatively avas- 

 cular area of the mesentery of the terminal portion of the ileum and embraced 

 within the ileo-colic artery and the lowest vasae intestini tenuis ; (/") hernia; through 

 the usual hernial apertures or regions of the parietes (page 1762); i^g) intussuscep- 

 tion, one form of which is due to irregular contraction of the circular fibres of the 

 muscular coat, so that as the peristaltic wave passes downward a segment of gut, 

 made smaller by this contraction, is forced into the portion immediately beneath it, 

 which is of larger calibre as a result of having failed to contract at the proper time ; 

 (Ji) pressure from 7uithout, as from tumors, which, as they must meet with counter- 

 resistance and relative fixity of the gut to produce constriction, most often affect the 

 duodenal (as in cancer of the pancreas), upper jejunal, or ileo-caecal segments; 

 (/) peritonitis, the relation of which to intestinal obstruction will be subsequently 

 explained (page 1756); (y) tumors of the intestines themselves, not very frequent in 

 the small intestine, but most often found at its two extremities. 



T\\G position of the different portions of the small intestine varies greatly. The 

 lower end of the duodenum, the upper end of the jejunum, and the lower end of 

 the ileum are the most fixed points. A description of the normal arrangement of 

 the coils of the jejuno-ileum has been given (page 1651). 



Of the duodenum only the first portion has been found involved in internal 

 herniae. The more or less vertical coils of the jejunum, and especially those of the 

 terminal portion of the ileum which occupy the pelvis when the bladder, rectum, 

 and sigmoid are not distended, are those most likely, for a priori reasons, to be 

 found in inguinal or femoral enteroceles, but clinical evidence in support of this is 

 not conclusive. In umbilical hernia the jejunum is apt to be involved, and the 

 gravity of this form of hernia, when strangulated, is supposed to be partly due 

 to this fact as well as to the effect upon the circulation of the constricted coil 

 produced by the sharp edge of the cicatricial tissue which surrounds the opening 

 and aggravated by the downward pull, through gravity, of the remainder of the 

 intestines. 



When the stomach is full the intestines are depressed ; when it is empty they 

 rise, so that in the left hypochondriac region they may be in contact with the dia- 

 phragm. If the colon is distended, the small intestine can occupy but little of the 

 lumbar, epigastric, or hypochondriac regions. Conversely, if the small intestine is 

 distended, it may so fill the pelvis and compress the rectum as to prevent the 

 passage of a tube or bougie into the sigmoid, and thus give rise to a mistaken diag- 

 nosis of obstruction at that point. If the spleen is enlarged, they are carried down- 

 ward and to the right ; if the liver, downward and to the left ; if the bladder or 

 uterus, upward. 



In ascites they are above the fluid, — i.e., in the umbilical region in the supine 

 and the epigastric region in the erect position. 



Normally the coils of the small intestine are closely applied to one another, and 

 this condition, by permitting of rapid adhesion, and thus of isolation of an infected 

 focus, has saved thousands of lives, especially in cases of appendicitis and pyosal- 

 pinx, and less frequently in cholecystitis and other forms of intra-abdominal infection. 



Operations. — The principles which should govern in opening the small intestine, 

 in avoiding or controlling hemorrhage, and in suturing wounds accidental or opera- 

 tive have been sufficiently explained (page 1653). 



The recognition of the duodenum is not difficult. It occupies portions of the 

 right hypochondriac, right lumbar, and umbilical regions. The spine of the second 

 lumbar vertebra is just above it. The hepatic flexure of the colon is anterior to it 

 at a point just below the ninth rib on the right side. The mesentery commences at 

 the duodeno-jejunal junction. A notch which can be felt in the peritoneum serves 

 as a guide to this particular part (Maylard). 



Duodenotomy may be required, either as an aid or as the main avenue of ap- 

 proach, in cases of impacted calculus in the common bile-duct (page 1732). It is 



