ABNORMAL CONDITIONS OF THE ABDOMI NAL CAVITY.-All the abnormal conditions of the abdomen may be considered under two heads : 1. as they regard the parietes of the cavity; arid, 2. as they refer to the positions of the contained organs. We shall first examine the abnormal conditions of the parietes.
Congenital malfOrmations qf the abdominal parietes.—The first class of these malformations which demands consideration is that which de pends on a defect in the development of the structures which form the abdominal walls, and these are by far the most numerous. In ex amining them it is to be bome in mind that many of the abdominal viscera exist before the walls of the cavity, which are formed around the viscera, and that the anterior wall is later in its formation than any of the others. The ca vity containing the viscera seems at first to be a continuation of that of the umbilical cord, its walls being continued from the sheath of the cord. A distinct separation does not appear to take place until the skin has become deve loped, when a line of demarcation is evident between the skin of the abdomen and the sheath of the cord.
The anterior wall may be deficient on both sides to a greater or less extent, the lateral and posterior being also more or less involved. The maximum is when the defect extends not only throughout the whole anterior abdominal wall, but also to that of the thorax, leaving all the viscera, of both abdomen and thorax visible, being covered only by a thin membrane; and frequently congenital deficien cies of the lower part of the anterior wall of the thorax are accompanied by a more or less ex tensive defect of the upper part of the same wall of the abdomen, and the heart is included with the abdominal viscera, which are rendered visible, and which, in some instances, protrude forwards. There may, however; be a con genital deficiency of, or fissure in the deeper seated elements of the anterior abdominal and thoracic wall, and yet the skin remain per fect and cover the protruded viscera.* But the thoracic parietes may be perfect, and yet there unity exist an imperfect condition of the abdominal parietes to a greater or less extent, which imperfection evidently results from the continuance of a greater or less portion of the abdominal wall in that condition in which it naturally exists in the early stages of fo?tal development. In such cases the viscera are
covered by an expansion which is continuous with the sheath of the umbilical cord. When the deficiency of the abdominal wall exists to a great extent, the tumour formed by the pro truding viscera is designated by the term even tration ; but if the defect be very limited, and exist, as it generally does, at the base of the umbilical cord, then the protrusion is an exom phalos or congenital umbilical hernia. Both, as Isidore Geoffroy St. Hilaire remarks, are results of an arrest in the development of the abdominal walls, with this difference, that in the former the cessa.tion of development takes place at an early period of fcetal existence, but in the latter at a late period. In conformity with the same laws, under the influence of which the arrest of development took place, we find that, as in the progress of the natural formation, the small iDtestine is the last to enter the abdominal cavity, so a larger or smaller portion of that intestine is generally found in the tumour of a congenital exom phalos. The nature of the contents of an eventration depends evidently on the extent of the deficiency and the region of the abdomen vvhich is most involved.
In some instances the peritoneum is deficient to an extent corresponding to that of the defi ciency of the abdominal parietes. This is a rare occurrence, and is generally met with where the defect of development is very extensive.* There are cases, however, where, although the defect was small, the peritoneum was absent to a corresponding extent, and the intestines protruded through the opening in a naked state.t The congenital inguinal hernia must likewise be referred to an arrest in the development of a very small portion of the anterior abdo minal wall. The canal of communication which at one period exists between the peri toneal sac and the sac of the tunica vaginalis remains pervious, the natural process by which it is closed having been arrested. This mode of explaining the formation of congenital bubo nocele does not preclude the possibility of its accidental occurrence, the material which closes the canal having given way under the influence of some force applied to it.