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the renal fascia by numerous connective tissue strands. These traverse the perinephric fat and undoubtedly assist in fixing the kidney in its place. The paranephric fat is present in greatest quantity behind the inferior part of the kidney, and in this position the layer of fibrous tissue, separating the two masses of fat and forming the posterior layer of the sheath of renal fascia, is usually well marked.

Fixation of the Kidney. The kidney is not held in its place by any distinct ligaments, or special folds of peritoneum, but its fixation depends, to a large extent, on the pressure and counter-pressure which is exerted upon it by neighbouring structures, and on its connexions with the fascia renalis above described.

Posterior Relations and the Posterior Surface of the Kidney.-The muscles of the posterior abdominal wall on which the kidney rests are the psoas major, the

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FIG. 981.-THE POSTERIOR RELATIONSHIPS OF THE KIDNEYS. The dotted lines indicate the contours of the kidneys. The drawing is made from a model prepared by the late Professor Cunningham.

quadratus lumborum, the diaphragm and the tendon of the transversus abdominis. The abdominal surfaces of these muscles do not lie on the same plane, but slope towards one another, and thus the bed on which the kidney rests is not flat. When but little fat is present, the posterior aspect of the kidney adapts itself to the inequalities of the surface against which it is placed, and so we may find on a kidney which has been carefully fixed and hardened before it has been disturbed,

areas marked off for the different planes of these muscles. When such a kidney is in position, slight ridges or elevations separating these areas correspond to the angles along which the different muscular planes meet. These ridges can be observed in the hardened kidney, after its removal from the body, but usually they are not sharply defined, the angles between the muscular planes being very obtuse.

A kidney removed from the body after having been hardened in situ (Fig. 982)

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presents an area along the medial part of its posterior surface adapted to the anterior aspect of the psoas major muscle. This part of the posterior surface looks medially and slightly posteriorly. More laterally there is a larger area which rests against the quadratus lumborum and looks more directly backwards. These two areas are separated by a rounded ridge which fits into the angle between the muscles mentioned. Beyond the area in contact with the quadratus lumborum is the thick lateral border of the kidney, which rests for the most part on the tendon of the transversus abdominis and on the diaphragm.

Towards the superior end of the kidney the posterior surface slopes somewhat forwards and rests upon the diaphragm. Indeed the superior part of the kidney is, as a whole, bent slightly forwards, following that part of the arch of the diaphragm on which it rests, and thus a narrow interval is left, in which the pleural cavity passes down behind the superior end of the kidney (Fig. 981). This relation

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FIG. 982.-THE POSTERIOR ASPECT OF THE KIDNEYS. Same specimen as Fig. 981. The dotted lines mark out the areas in contact with the various muscles forming the posterior abdominal wall.

ship of the pleural cavity to the kidney is of great importance in connexion with surgical operations performed through a lumbar incision. The portions of the diaphragm to which the kidney is applied are the crus and the parts arising from the last rib and lumbo-costal arches.

The posterior relationships of the kidney are well seen in Fig. 981.

In addition to these surfaces, or "facets," for the muscles with which it is in contact, the posterior aspect or lateral border of the kidney often shows a groove for the last rib, another for the lateral lumbo-costal arch, and two or three depressions for the tips of the transverse processes of the upper two or three lumbar vertebræ. In some cases also faint narrow grooves are to be seen for the nerves which pass downwards and laterally between the kidney and quadratus lumborum-namely, the last thoracic nerve and the ilio-hypogastric and ilio-inguinal nerves.

It is probable that some at least of the depressions on the posterior aspect of the kidney are produced after death, and are caused by the weight of the other abdominal organs pressing the kidney backwards against the more resisting structures of the abdominal wall, at a time when the muscles behind the kidney have become flaccid. When much fat is present the posterior aspect of the kidney is more uniformly convex.

The lateral border in its middle and inferior part is rather a surface than a border, and looks for the most part directly backwards. It rests on the diaphragm and on the anterior surface of the tendon of the transversus abdominis, to the

lateral side of the quadratus lumborum muscle. The lateral border is narrowest above, and widest just below its middle point, corresponding to the greater thickness of the kidney at this level.

In many ways it would be more satisfactory to apply the term facies muscularis or muscular surface collectively to the areas above described as "posterior surface' and "lateral border"; in like manner the term facies visceralis, or visceral surface, might be suitably applied to the so-called anterior surface of the organ. The edge separating the visceral from the muscular surface is the actual lateral edge or border of the kidney.

Anterior Relations and the Anterior Surface of the Kidney. The anterior relations of the kidneys not only differ on the two sides of the body, but also many

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FIG. 983.-DISSECTION TO SHOW THE RELATIONSHIPS OF THE KIDNEYS AND OF THE URETERS

TO THE MUSCLES OF THE POSTERIOR ABDOMINAL WALL.

of the structures related to the anterior surface of each kidney undergo frequent changes in position during life. Hence it is not possible to give more than a general account of the anterior relationships of the kidneys.

Right Kidney. A small area on the superior part of the anterior surface of the right kidney is in relation to the corresponding suprarenal gland (Fig. 983). The rest of the superior part of the anterior surface is in contact with the visceral surface of the liver, which is often hollowed out to form a fossa for the kidney. The suprarenal gland is bound to the kidney by connective tissue, while the part of the kidney in relation to the liver is, like the liver itself, covered by peritoneum, and thus the two organs, although closely applied, are really separated by a part of the general peritoneal cavity. Immediately anterior to the inferior end of the right kidney are usually found two parts of the alimentary canal-namely, the descending part of the duodenum and the right flexure of the colon, or the

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commencement of the transverse colon. The part of the kidney related to the duodenum lies to the medial side of the area which touches the colon, but the exact amount of the kidney in contact with each of these two parts of intestine varies much in different subjects. Frequently the colon and the kidney are both covered by peritoneum where they are in contact, but the duodenum is bound down to the kidney by connective tissue. In addition to the structures mentioned, some portion of the ileum, or of the jejunum, is often found in contact with a small part of the right kidney near its inferior end.

In some cases the peritoneal membrane does not cover the whole of the surface in contact with the liver, and then the superior part of the hepatic area of the kidney is, like the anterior aspect of the suprarenal gland, bound by connective tissue to the "uncovered" area on the posterior aspect of the liver.

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Hepatic area.

Duodenal area

Colic area

Crista iliaca

Ureter

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-Splenic area

Pancreatic

area

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Colic area

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FIG. 984.-ANTERIOR ASPECT OF THE KIDNEYS AND GREAT VESSELS. The drawing was made, before removal of the organs, from a specimen in which the viscera had been hardened in situ. The dotted lines mark out the areas which were in contact with the various other abdominal viscera.

Left Kidney. The extreme superior and medial part of the anterior aspect of the left kidney is united by connective tissue to the lower part of the left suprarenal gland, and the area immediately below this is in contact with the stomach and the pancreas. The pancreas, like the suprarenal gland, is bound down to the kidney by connective tissue, but the stomach is separated from the area with which it is in apposition by a portion of the omental bursa. The area in actual contact with the stomach is a small somewhat triangular district situated above the level at which the pancreas is related to the kidney. The superior and lateral part of the anterior aspect of the kidney is related to the spleen, the two organs being separated by a portion of the general peritoneal cavity, except along the area where spleen and kidney are connected by the lieno-renal ligament. The anterior surface of the inferior end of the left kidney is related, towards the medial side, to a part of the jejunum, and, towards the lateral side, to the left flexure of the colon or to a part of the descending portion of the colon. In most cases, however, the colon lies against the posterior abdominal wall to the lateral side rather than on the anterior surface of the left kidney.

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the vena portæ. In the sixth week, these two rudiments meet and unite with one another, forming a long slender glandular mass which passes backwards within the dorsal mesogastrium (meso-duodenum), between the vertebral column and the greater curvature of the stomach. The pancreas, so formed, follows the changes which occur in the position of the stomach and of the dorsal mesogastrium. Consequently its free dorsal extremity comes to be directed to the left, while the right extremity or head is included within the hollow of the curve formed by the duodenum. At first, it possesses a dorsal mesentery, a part of the dorsal mesogastrium, but from the fifth month this disappears, coincidently with the rotation of the gland into the transverse axis of the body.

The lower part of the head, the body, and tail of the gland arise from the ventral element, and the upper part of the head arises from the dorsal bud.

The primary diverticula give off buds, lined with cylindrical epithelium, and these in turn give off other buds, and the process goes on until the mass of the gland is formed. The islets of Langerhans are formed at a very early stage, from the entodermal lining cells of the branching diverticula which form the gland acini.

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