1. Defect And Excess Of Formation

Arrest of development in the peritoneal sac occurs in the shape of fissure in the mesial line, or external to it; in the case of the diaphragm being absent, of a fusion with the pleura; as defective development of the mesentery at various points, as defective development or complete absence of several other folds, the omentum, the appendices of the omentum, as deficiencies in these parts, etc.

1 Oestr. Jahrb. xxi. 2.

Excess of development frequently occurs in the shape of unusual length of the duplicatures, e. g. of the omentum, the mesenteries, etc, or of supernumerary folds and peritoneal pouches. These are chiefly found in the hypogastric, and more especially in the iliac and in the inguinal regions, and near the fundus vesicae. There is access to these sacs by a well-defined fissure or ring, which is frequently surrounded by a tendinous band, lying in the duplicature. In the case of their inclosing portions of the intestine, they may give rise to internal incarceration, which, on the one hand, resembles external hernia, on the other, does not afford the diagnostic signs peculiar to this affection, and may, therefore, be considered as forming a transition between external and internal hernia. Similar formations, such as a delicate serous envelope of the small intestine, must be explained by an original anomaly in the development of the peritoneum.

2. Anomalies In The Size And Form Of The Peritoneal Sac

Among these we reckon a general increase of the peritoneal surface, corresponding with a congenital enlargement of the abdominal cavity and the intestines; the acquired extension, which may be uniform, as the result more especially of an accumulation of serous fluid (ascites); or partial, as presented to us in congenital or accidental hernia, and in the abnormal size or acquired elongation of single folds; the latter are brought about by dislocations of the abdominal contents, which arise spontaneously, or from a variety of causes, are most frequently seen affecting the mesenteries and the omentum, and are of signal importance in reference to the causation of internal hernia.

A small peritoneum is the result of an arrest of development in the abdominal cavity, subordinate to the development of the pleura; an apparent diminution may be caused by dislocation of the abdominal contents, as in large scrotal or diaphragmatic hernia.

The anomalies of form are involved in the above anomalies of size.

3. Solutions Of Continuity

The peritoneal sac is liable to solutions of continuity from penetrating wounds of the abdomen, from the effect of powerful concussion, of excessive bodily exertion, from spontaneous ruptures of the hollow or parenchymatous organs it invests, in consequence of traumatic injuries, from contusion, rupture, and separation of the subjacent tissues. The extent and nature of the injury vary as much as its situation.

4. Abnormities Of The Tissues

1. Hyperaemia

Hyperaemia is either general, or, when caused by the congested state of an organ invested by the peritoneum, partial. It gives rise, on the one hand, to an increase of secretion and to dropsical accumulations in the peritoneal cavity; on the other, to hypertrophy and thickening of the serous tissue, and to the development of a subserous fibroid or fibro-chondroid growth. The peritoneal investment of the spleen offers the best illustration of the latter.