The intestinal canal may be irregular in position, either being placed altogether external to the abdominal cavity, or by its relations and its disposition within the cavity being irregular.

In the first class we reckon the following congenital irregularities: protrusion of the intestines, external to the abdomen, from absence of the parietes, or from fissure at or near the median line (eventration, omphalocele, congenital umbilical hernia); congenital inguinal hernia; thoracic hernia from partial or total absence of the diaphragm, the left side of the latter being chiefly liable to this malformation. To the acquired irregularities belong prolapsus of the intestines, resulting from penetrating wounds of the abdomen, wounds or rupture of the diaphragm, and the different forms of ordinary hernia.

In the second class we reckon, as a congenital deviation, the lateral transposition which is likely at the same time to involve secondarily, not only the other abdominal, but also the thoracic viscera; the various changes of position, produced by diffused or circumscribed fluid effusions or accumulations, by hypertrophied viscera, or by morbid growths; the spontaneous descent of the transverse colon into the hypogastric region, of the small intestine into the pelvic cavity; external and so-called internal hernia; invagination and prolapsus ani, the two being identical in character and causation; the changes of position which the intestine experiences in consequence of the cellular or fibro-cellular adhesions that it forms with the parietes, and that unite the coils to one another.

For external hernia we refer the reader to surgical works; we shall here examine only the relations of internal hernia, invagination, prolapsus ani, and the change of position produced in the intestines by adhesion.