Figure 13.15 A. A 9-mm embryo (approximately 36 days). The liver expands caudally into the abdominal cavity. Note condensation of mesenchyme in the area between the liver and the pericardial cavity, foreshadowing formation of the diaphragm from part of the septum transversum. B. A slightly older embryo. Note the falciform ligament extending between the liver and the anterior abdominal wall and the lesser omentum extending between the liver and the foregut (stomach and duodenum). The liver is entirely surrounded by peritoneum except in its contact area with the diaphragm. This is the bare area of the liver.
Pyloric stenosis occurs when the circular and, to a lesser degree, the longitudinal musculature of the stomach in the region of the pylorus hypertrophies. One of the most common abnormalities of the stomach in infants, pyloric stenosis is believed to develop during fetal life. There is an extreme narrowing of the pyloric lumen, and the passage of food is obstructed, resulting in severe vomiting. In a few cases the pylorus is atretic. Other malformations of the stomach, such as duplications and a prepyloric septum, are rare.
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