224 DIGESTIVE ORGANS of the urethra, and iirthe female that of the vagina also. The anterior boundary is formed above by the muscles of the anterior abdominal wall and the fascia transversalis ; the linea alba occupies its middle line, and about the middle of the linea alba is the umbilicus or navel ; the anterior wall below is formed by the two pubic bones with the symphysis. The lateral walls, or flanks, are formed above by the flat muscles of the abdominal wall and the fascia transversalis, and below on each side by the ilium and ischium with the muscles attached to them. The posterior wall is formed by the lumbar spine, sacrum, and coccyx, and by the muscles attached to these bones with their accompanying fascia;. The abdomen is primarily divided into the pelvis and abdomen proper. The pelvis is subdivided into the false pelvis, or the part above the pelvic brim, and true pelvis, or part below the pelvic brim. n- The Peritoneum is the largest and most complicated serous mem- H.-UHI. brane in the body. Like the other serous membranes, it not only lines the walls of the cavity in which it is situated, but gives a more or less complete investment to the contained viscera. It is arranged, therefore, so as to form a parietal and a visceral part, which are continuous with each other in the various regions where the part lining the wall is reflected as a covering upon the viscera. A space or cavity, called the peritoneal cavity, is inclosed between the parietal and visceral layers. This cavity, as in other serous mem branes, is a closed or shut sac, without any communication externally, except in the female, where the two Fallopian tubes open into it. Through these openings the mucous membrane lining the tubes becomes continuous with the serous membrane, and a communication is established between the lumen of each tube and the peritoneal cavity. That surface of both the parietal and visceral portion of the peritoneum which lies next the cavity is free, smooth, covered by an endothelium, and lubricated by a little serous fluid, which under some pathological conditions may be greatly increased iu quantity, so as to cause abdominal dropsy. The moistening of the two free surfaces by the serum permits them to glide smoothly on each other, during the movements of the viscera, and the changes which take place in their size and position. The opposite surface of the peritoneum is attached that of the parietal part to the fasciae situated internal to the abdominal muscles, that of the visceral part to the subjacent coat of the several organs. Special names are applied to the folds or duplicatures of the peri toneum, which pass from the wall of the abdomen to the viscera. In the case of the liver, spleen, bladder, and uterus, these folds are named ligaments, whilst the corresponding folds which pass to the intestine have received the name of mesenteries. Folds of peri toneum also pass between certain of the viscera themselves, and these are called amenta. >mach. The Stomach is the bag-like dilatation of the alimentary canal, connecting the oesophagus with the duodenum, in which the food is mingled with the gastric juice, and con verted into a pulpy substance the chyme. The stomach is situated in the costal zone of the abdominal cavity ; three-fourths of its volume being contained in the left hypochondrium, whilst the remaining fourth extends into the epigastrium. About five-sixths of the organ lies to the left of the mesial plane, and one-sixth to the right. The stomach varies in size, shape, and somewhat in position, according as it is empty or full of food. When moderately full it is about 1 foot in length, whilst its greatest transverse diameter is 4 to 5 inches. Its general shape is pyrifonn, and it may be described as possessing two extremities, two surfaces, and two borders. The larger extremity, called the fundus, cardiac extremity, or great cul-de-sac, is directed upwards so as to be in contact with the under surface of the diaphragm, whilst the smaller end, the pyloric or duodenal extremity, is directed downwards, curves to the right, and becomes continuous with the duodenum. The surfaces form the anterior and posterior tvalls of the stomach. When the organ is empty, the walls are flattened, and in apposition with each other by their inner surfaces ; but when it is distended they are convex, The borders of the stomach are curved and unequal in size ; one is convex, about three times as long as the other, and is named the greater curvature ; the other is concave, and forms the lesser curvature. The curvatures are so arranged that the greater has its convexity directed downwards and to the left, where it lies in relation to the transverse colon and the splenic flexure of the colon. The lesser curvature has ks concavity directed upwards and to the right, and the oesophagus opens into the stomach at the upper end of the lesser curvature. Above this orifice the stomach expands into the fundus, which is situated in the highest part of the left hypochondrium, and occupies therefore the summit of the vault of the left half of the diaphragm. At the lower and right end the two curvatures lie almost horizontally in the epigastrium and terminate at the pylorus, where the stomach becomes continuous with the duodenum. The pylorus, or gate of the stomach, is situated in the epigastrium about three fingers breadth below the ensiform cartilage, and immediately to the right of the mesial plane. The junction of the stomach with the duodenum is marked by a circular constriction externally, called the pyloric constriction, and by a valve internal!} , the pyloric valve. At its pyloric end the stomach presents a small bulging, the lesser cul-de-sac, or antrum pylori. The stomach is retained in position, partly by its con nections with the oesophagus and duodenum, partly by the pressure of the surrounding abdominal walls and viscera, and partly by folds of peritoneum which pass from it to the adjacent structures. These folds are as follows : The gastro-phrenic ligament extends from the diaphragm to the stomach in the angle between the oesophagus and the cardiac extremity ; the gastro-hepatic or small omentum passes from the lesser curvature of the stomach to the lips of the transverse fissure of the liver ; the gastro-splenic omentum from the cardiac end of the stomach to the spleen ; the gastro-colic or great omentum descends from the greater curvature of the stomach in front of the coils of the small intestine, and then ascends to inclose the transverse colon. Structure of the Stomach. The wall of the stomach consists of four coats, named, from without inwards, serous, muscular, submucous, and mucous coats. The external or serous coat is that part of the peritoneal membrane which incloses the stomach, one layer covering the anterior, the other the posterior surface. It leaves the stomach at the curvatures, where it forms the great and small omenta, and along these borders the two layers inclose between them the blood-vessels and nerves which supply the organ. The muscular coat consists of non-striped fibres arranged in three layers from without inwards. The outer layer consists of longitudinal fasciculi, which are continuous with the external longitudinal layer of the oesophagus. They form scattered fasciculi extending longitudinally over the surface of the stomach from cardia to pylorus; but alon^ the two curvatures, more especially the lesser, they are col lected into stronger bundles, and at the pylorus they become continuous with the longitudinal fibres of the duodenum. The middle layer consists of circular fasciculi, which form a ring-like arrangement transversely to the long axis of the stomach. These fasciculi are comparatively thin and scattered at the cardiac end, but as they approach the pylorus they become more closely aggregated, so as to form a thick layer, which at the pylorus extends into the pyloric valve, and forms the sphincter pylori muscle. The circular fibres of the stomach are in the same morphological plane as the circular fibres of the oesophagus and duodenum. The inner layer consists of oblique fasciculi, which are not found over the entire organ ; the greater number spring from the left side of the cardiac orifice, and radiate on the anterior and posterior surfaces towards the pylorus and greater curvature. These oblique fibres by their contraction approximate the cardia to the pylorus, the great curvature to the smaller, and the anterior to the posterior wall; they are thus the true grinding muscles of the stomach, and have been compared to the muscular gizzard of the bird. From the relation of the two groups of oblique fibres to the cardiac orifice they probably close that opening during
gastric digestion. The longitudinal and circular fibres