Complete absence may occur, but incomplete development is more common. There may be stenosis anywhere. The rectum may end in a blind sac, atresia ani, either low down or up in the sigmoid flexure. Cloaca formation refers to a condition in which there may be one common cavity acting as an outlet for the rectum and genito-urinary tracts. Diverticula, localized dilatations, are quite frequent, particularly Meckel's diverticulum. This is found in the ileum about three feet above the ileocecal valve. It is a finger-like projection of the same histologic formation as the intestine; is the remains of the omphalomesenteric duct. It may be adherent at the umbilicus, remain open, and allow feces to escape. Acquired diverticula may be present as small projections from the exterior of the gut, usually near the mesenteric attachment. They consist of mucous membrane and serosa, the muscular coat being absent. Occasionally inflammation, diverticulitis, with abscess formation, perforation and peritonitis may follow. Adhesions, also, may form with adjacent structures. Enterocysts are dilatations of the omphalo-mesenteric duct. There may be a transposition of the intestines, the colon ascending on the left and descending on the right. There is frequently an abnormal course of the large intestine, particularly of the transverse colon. This, instead of going directly across the upper part of the abdomen, takes a V-shaped course, the apex of the curve frequently extending as low as the pubes.

Hernia of the intestines refers to the abnormal entrance into or the passage through an opening.

Herniae may be due to a weakening of the abdominal walls or to the failure of a canal to close. The mesentery may be longer than usual and allow very free motion, or there may be an abnormal amount of fat, causing an increase of weight. The exciting cause in most cases is sudden exertion, or it may be the result of repeated strains.

Herniae may be external or internal, congenital or acquired.

External are those in which the hernial sac lies outside of the abdomen. Internal are those in which the sac lies within one of the cavities within the body.

The sac may contain only a portion of the small intestine or there may be some of the large abdominal organs present. There is generally a constriction (neck) at the point where the sac passes from the peritoneal cavity; below is a dilated pouch. The inner wall of the sac is composed of the peritoneum.

A hernia is reducible if it can be pushed back through the opening from which it escaped. If it cannot be returned it is an irreducible hernia. The reduction may be prevented by adhesions having formed at the neck of the sac, by the accumulation of fecal matter, by edema or other causes. There may be such a constriction at the neck as to interfere with the circulation, a strangulated hernia. This may result from the same conditions, in a more severe degree, as cause an irreducible hernia, or from the entrance of more viscera into the sac. It is followed by an extreme passive congestion, inflammation of neighboring tissues, and hemorrhage and gangrene. If the strangulation is relieved early before degenerative changes have set in, the intestine may resume its usual condition.

In old hernias a chronic inflammatory process may have gone on, with the formation of fibrous adhesions between the sac and neighboring coils of intestine. This is due to the circulatory disturbances resulting from the twisting or stretching of the vessels.

Obstruction of the intestine may be due to the presence of foreign bodies within its lumen, to fibrous adhesions and bands, to a twisting or volvulus, to intussusception or invagination, or as a result from the formation of cicatrices at the seat of ulcerations. It may be complete or incomplete, acute or chronic. If the obstruction has been a chronic one, there will probably be some dilatation of the intestine above the constricted area. In time there may be hypertrophy of the walls with inflammation and ulceration. The part below may become atrophic.