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separated by an intervening depression. Into the right cupola fits the greater part of the liver; in the left lie a part of the stomach and spleen. On the superior surface of each cupola is placed the base of the corresponding lung, whilst between them, on the depression, rests the inferior surface of the heart.
During expiration, the right cupola ascends almost to the level of the right nipple; it is highest at a point about one inch medial to the nipple line, and here it reaches the superior border of the fifth rib, or even the middle of the fourth intercostal space. On the left side it is one-half to one inch (12-25 mm.) lower, and in the median plane it crosses the inferior extremity of the body of the sternum about the level of the seventh rib cartilage (Fig. 912).
Below, the cavity is continued into the cavity of the pelvis minor.
The anterior wall is formed by the aponeuroses of the three flat abdominal muscles, obliquus externus, obliquus internus, and transversus abdominis, together with the two recti, which latter constitute powerful braces for the wall, on each side of the median plane.
Anteriorly, below the junction of abdomen and pelvis, lies the pubic symphysis The body of the pubis looks upwards as well as posteriorly, and appears to form a support or floor for the viscera contained within the anterior part of the abdominal cavity.
The side walls are formed by the muscular portions of the obliqui and transversi muscles, and below by the iliac bones and the iliacus muscles.
Finally, the cavity is limited posteriorly by the lumbar portion of the vertebral column, with the crus of the diaphragm and psoas major muscle on each side, and the quadratus lumborum still more laterally. The iliac bones also enter into the formstion of the inferior portion of the posterior wall.
The superior portion of the cavity lies under cover of the ribs, which afford considerable protection to that part of the abdomen, particularly at the sides and
posteriorly, in which latter position the cavity is further protected by the vertebral column. Anteriorly, on the other hand, the ribs are wanting below the sternum, and there the abdominal wall is formed only of aponeuroses and muscles. But even at the sides and back there is a considerable zone, usually one to two inches wide, between the lower ribs above and the crest of the ilium below, which has no bony support except that afforded by the vertebral column.
Whilst the circumference of the diaphragm is attached to the inferior part of the thoracic framework anteriorly and laterally, and to the lumbar vertebræ posteriorly, the central portion of the dome, on the other hand, namely, the central tendon, is placed high up, under cover of the ribs, and in a more or less horizontal plane. As a result, the peripheral muscular part slopes upwards and medially from the circumference of the thoracic framework to the central tendon, and lies for a considerable distance in contact with the deep surface of the ribs; thus the diaphragm comes to form, not only the roof of the cavity, but it also enters into the formation of the sides, the posterior wall, and, to a less extent, of the anterior wall; and almost as much of the cavity of the abdomen as of the thorax lies under shelter of the ribs.
Owing to the fact that the boundaries of the abdomen are formed chiefly of muscles, it follows that its walls are capable of contraction to a very considerable extent, and the size of the cavity can consequently be altered in all directions. Its chief changes in form are due to the descent or elevation of the diaphragm, the contraction or relaxation of the anterior wall and the side walls, and the raising or lowering of the pelvic floor.
The superior aperture of the pelvis minor (Figs. 234 and 235, p. 236), which separates the two natural divisions of the cavity, is formed behind by the base of the sacrum, at the sides by the linea terminalis of each hip bone, and in front by the pubic crests and the symphysis pubis. In the erect position it usually makes an angle of about 55 to 60 degrees with the horizontal. The two portions of the abdominal cavity which the superior aperture separates meet at an angle, the abdomen proper extending almost vertically upwards from it, whilst the pelvic cavity slopes backwards and slightly downwards.
The pelvic cavity is bounded in front and at the sides by the portions of the hip bones below the level of the linea terminalis. Those portions of the bony wall are partly clothed by the obturator internus muscles, and, internal to those muscles, by the parietal portion of the pelvic fascia, as low down as the arcus tendineus. The posterior wall is formed by the pelvic surface of the sacrum, covered on each side by the piriformis muscle. That wall (as represented by the piriformes muscles) meets the side wall at the anterior border of the greater sciatic foramen; through that foramen the piriformis passes out, thus closing up what would otherwise be a large aperture in the parietes of the cavity. The floor is composed of the two pairs of muscles which form the pelvic diaphragm, namely, the levatores ani and the coccygei-covered by the visceral layer of the endopelvic fascia. Those muscles pass, on each side, from the side wall of the pelvis, downwards and medially towards the median plane, and present a concave superior surface towards the pelvic cavity.
Within the muscles forming its walls, the abdomen is lined by an envelope of fascia, which separates the muscles from the extraperitoneal connective tissue and peritoneum. That fascial layer is distinguished in different localities as:-(1) the fascia transversalis, on the anterior wall and the side walls, lining the deep surface of the transversalis muscle and continuous above with the fascia clothing the inferior surface of the diaphragm; (2) the fascia iliaca, on the posterior wall, covering the psoas and iliacus muscles; (3) the fascia diaphragmatica, covering the inferior surface of the diaphragm; and (4) the fascia endopelvina, lining the pelvis.
Apertures. Certain apertures are found in the walls of the abdomen, some of which lead to a weakening of the parietes. They are: the three openings in the diaphragm for the passage of the inferior vena cava, the oesophagus, and the aorta, respectively; the apertures in the pelvic floor, through which the rectum, the urethra, and the vagina in the female, reach the surface; the inguinal canal, through which the spermatic funiculus (or the round ligament) passes, in leaving the abdominal cavity; and lastly, the femoral canal, a small passage which extends downwards from the abdomen along the medial side of the femoral vessels. The latter two,
particularly, constitute on each side weak points in the abdominal wall, through which a piece of intestine occasionally makes its way, giving rise to inguinal or femoral hernia respectively. Similar protrusions may also occur at other points in the abdominal wall, and also through apertures in the pelvic wall.
Tela Subserosa (O.T. Extraperitoneal or Subperitoneal Connective Tissue).— Between the fascia which covers the deep surfaces of the abdominal muscles, and the peritoneum which lines the cavity, there is found a considerable quantity of connective tissue, generally more or less loaded with fat, which is known as the tela subserosa. It is part of an extensive fascial system which lines the whole of the body cavity, outside the various serous sacs, and it is continued on the several vessels, nerves, and other structures which pass from the trunk into the limbs and neck.
In the abdomen it is divisible into a parietal and a visceral portion, both composed of loose connective tissue. The former lines the cavity, whilst the latter passes forwards between the layers of the mesenteries and other peritoneal folds to the viscera. The two portions of the extraperitoneal tissue are perfectly continuous with one another, and contain in their whole extent a vascular plexus, through which a communication is established between the vessels of the abdominal wall, on the one hand, and those of the contained viscera, on the other.
The parietal portion is thin and comparatively free from fat over the roof and anterior wall of the abdomen, and there the peritoneum is more firmly attached than where the tissue is fatty and large in amount. In the pelvis minor, on the other hand, the tissue is loose and fatty, and, as such, it is continued up for some inches on the anterior abdominal wall above the pubes, to permit of the ascent of the bladder during its distension, in the interval between the peritoneum and the anterior abdominal wall. There also the urachus and the obliterated umbilical arteries will be found passing up in its substance. On the posterior wall the tissue is large in amount and fatty, particularly where it surrounds the great vessels and the kidneys.
From the parietal portion the visceral expansions are derived, in the form of prolongations around the various branches of the aorta. Those expansions are connected with the areolar coats of the blood vessels and are conducted by them into the mesenteries and other folds of the peritoneum, and thus reach the viscera.
The chief uses of the tela subserosa are: (1) to unite the peritoneum to the fascial and muscular layers of the abdominal wall; (2) to connect the viscera to those walls and to one another in such a loose manner that their distension or relaxation may not be interfered with. That would not be the case if the connecting medium were firm or rigid; (3) in addition, it is a storehouse of fat, forms sheaths for the vessels and nerves, and establishes, through its vascular plexus, communication between the parietal vessels and those distributed to the abdominal viscera.
Subdivision of the Abdomen Proper.-Owing to the large size of the cavity and in order to localise more correctly the position of the various organs contained within it, the abdomen proper is artificially subdivided by two horizontal and tw sagittal planes (Fig. 913).
Of the two horizontal planes, one divides the trunk at the level of the lower border of the tenth costal cartilage; this is known as the subcostal plane, and the line where it intersects the abdominal wall is the subcostal line. The second horizontal plane is at the level of the highest point of each iliac crest which is visible from the front; this point corresponds to the tubercle seen on the external lip of the crest, about two inches posterior to the anterior superior spine, and car be easily located; the line and plane are consequently known as the intertubercular line and plane, respectively.
The sagittal planes are drawn, one on each side, perpendicularly upwards from a point on the inguinal ligament midway between the anterior superior spine and the symphysis pubis. The planes and the corresponding lines are known as the lateral planes and lines respectively.
By the two horizontal planes the abdomen is divided into three zones, a superio: or costal, a middle or umbilical, and an inferior or hypogastric zone. By the tw
perpendicular planes each zone is subdivided into three regions, a central and two lateral. Thus, in the upper zone, we get a hypochondriac region or hypochondrium on each side, and an epigastric region or epigastrium in the centre. Similarly, the umbilical zone is divided into right and left lumbar regions, with an umbilical region between. And the hypogastric zone has a hypogastric region or hypogastrium in the centre, with right and left iliac regions at the sides.
In addition, the portion of the abdominal wall above the body of the pubis is known as the suprapubic region, and that immediately above the inguinal ligaments as the inguinal region.
The three central divisions, namely, the epigastric, umbilical, and hypogastric
FIG. 913.-PLANES OF SUBDIVISION OF THE ABDOMINAL CAVITY, AND OUTLINE TRACING OF THE LIVER, STOMACH, AND INTESTINE IN RELATION TO THE ANTERIOR ABDOMINAL WALL.
The oblique position of the stomach and the high position of the transverse colon are largely due to the fact that the subject was in the horizontal position.
regions, can conveniently be further subdivided by the median sagittal plane, passing through the middle of the body, into right and left halves.
The superior horizontal, or subcostal, plane passes posteriorly, through the superior part of the third lumbar vertebra, or the fibro-cartilage between the second and third lumbar vertebræ. The intertubercular plane cuts through the middle or superior part of the fifth lumbar vertebra. The inferior margin of the tenth costal cartilage frequently corresponds to the most dependent part of the thoracic framework. Often, however, the eleventh costal cartilage descends to inch lower. Nevertheless, the tenth cartilage is selected in drawing the subcostal plane, for two chief reasons, namely, it is visible from the front as a rule, and it is comparatively fixed, whilst the eleventh, being a floating rib, is much more movable, is variable in length, and more difficult to locate.
Another plane which is of some practical value is the transpyloric plane (Addison). This is a horizontal plane which is taken to intersect the trunk at the level of the first lumbar vertebra. That level is ascertained during life by taking the mid-point of a line drawn, on the surface of the trunk, from the superior border
of the sternum to the upper border of the symphysis pubis. The same level is obtained usually, but not so accurately, by taking the mid-point of a line drawn. from the xiphi-sternal articulation to the umbilicus.
Contents of the Abdomen.-The following structures are found within the abdominal and pelvic cavity:
1. The greater part of the alimentary canal, viz., stomach, small intestine, and large intestine. 2. Digestive glands: the liver and pancreas.
3. Ductless glands: the spleen and the two supra-renal glands.
4. Urinary apparatus: the kidneys, ureters, bladder, and part of urethra.
5. The internal generative organs, according to the sex.
6. Blood vessels and lymph vessels, and lymph glands.
7. The abdominal portion of the cerebro-spinal and sympathetic nervous systems.
8. Certain fatal remains.
9. The peritoneum-the serous membrane which lines the cavity, and is reflected over most of its contained viscera.
The arrangement of the peritoneum is so complicated, and its relations to the abdominal contents so intricate and detailed, that it will be expedient to postpone
its complete description unti the various organs, with their special peritoneal relations, have been separately considered. Nevertheless, it will be necessary to give here a general account Foramen epi- of the disposition of the membrane, and to refer to some of the folds which it forms in passing from organ to organ, or from these to the abdominal wall.
The peritoneum is the serous membrane which lines the abdominal cavity and invests most of the abdominal viscera, to a The mesentery greater or less degree. Like the pleuræ, pericardium, and other serous sacs, its walls are composed of a thin layer of fibrous tissue, containing numerous elastic fibres, covered over on the Recto-uterine side turned towards the cavity of the sac by a layer of flattened endothelial cells forming the tunica serosa. Like them, too the peritoneum in the male is a completely closed bag, but in the female this is not the case, for the ostium abdominale of each uterine tube opens into the sac. whilst the ostium uterinum of that tube communicates with the interior of the uterus, and thus indirectly, with the exterior of the body. Normally the membrane secretes only sufficient moisture to lubricate its surface, otherwise the sac is perfectly empty, and its opposing walls lie in contact, thus practically obliterating its cavity.
FIG. 914.-DIAGRAMMATIC MEDIAN SECTION OF FEMALE BODY, to show the peritoneum on vertical tracing. The great sac of the peritoneum is black and is represented as being much larger than in nature; the bursa omentalis is darkly shaded; the peritoneum on section is shown as a white line; and a white arrow is passed through the foramen epiploicum from the great sac into the bursa omentalis.
The use of these lubricated and highly polished serous linings, found in the