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THE kidneys, or glands which secrete the urine, are a pair of almost symmetrically placed organs, situated in the posterior part of the abdominal cavity, one on each side of the lower movable portion of the vertebral column. The fluid, or urine, secreted by the kidneys is received into the upper expanded portions of a pair of long tubes, the ureters, and by them it is conducted to the bladder, which is placed within the pelvic cavity. From the bladder the urine is passed, during micturition, along a passage called the urethra to the exterior. În the male the urethra is a relatively long passage, and traverses the prostate gland and the whole length of the penis; in the female it is a short tube, and opens on the surface just above the vaginal orifice.


The kidney (ren), when removed from a fresh subject, presents a bean-shaped contour. It is of a dark brown-red colour, and is surrounded by a thin glistening capsule, the tunica fibrosa, which gives to the whole organ a uniformly smooth surface. The kidney is not a solid body, but contains a cavity called the sinus renalis, the opening into which, termed the hilum renale, is situated on the medial and anterior part of the organ. Each kidney measures about 4 inches in length, 2 inches in width, and about 11 inches in thickness, and is placed so that its long axis is nearly vertical. The weight of the adult kidney is about 4 ounces. In the freshly removed kidney the superior and inferior,ends are smoothly rounded, and the extremitas superior or superior end is usually a little more bulky than the extremitas inferior or inferior end. The margo lateralis or lateral border, which is opposite the hilum, is rounded and convex, while the margo medialis or medial border, on which the hilum is placed, is concave from above downwards. These two borders separate the facies anterior or anterior surface from the facies posterior or posterior surface of the kidney.

The capsule, which envelops the whole organ, divides in the region of the hilum into two layers, one of which is continued over the lips of the hilum into the interior of the kidney, and lines the walls of the renal sinus. The other layer is prolonged to form a tubular sheath for the vessels and nerves of the kidney before they pass through the hilum to enter the sinus, within which they break up into branches. These branches, piercing the wall of the sinus, enter the substance of the kidney. The upper expanded portion of the ureter leaves the sinus, through the hilum, in company with the blood-vessels and


Position of the Kidneys. The precise level of the kidney in the abdominal cavity is subject to a considerable amount of variation, and, further, it is usual to find a difference in the level of the right and left kidney in the same individual. Most frequently the left kidney is on a somewhat higher level than the right, but in many cases the kidneys are found to occupy the same level, or, the more usual condition being reversed, the right kidney is a little higher than the left.

If a line is drawn round the body at the level of the lowest part of the thoracic wall, the whole, or almost the whole, of the left kidney will be found to lie above the level of the subcostal plane so determined. It is, therefore, situated in the subcostal zone of the abdominal cavity. The right kidney, however, although it lies for the most part in the subcostal zone, usually projects at its inferior part somewhat below the subcostal plane, and hence lies to some extent in the umbilical zone. It is often stated that the kidneys are placed on a somewhat lower level in the female than in the male subject.

By far the greater part, usually two-thirds or more, of the kidney lies to the medial side of a line drawn vertically upwards through the middle point of the inguinal ligament.

The posterior aspect of the kidney is closely applied against the muscles attached to the bodies of the last thoracic and upper three lumbar vertebræ, and is placed in front of the last rib and of the transverse processes of the upper three

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FIG. 979.-DISSECTION TO SHOW THE RELATIONSHIPS OF THE KIDNEYS. The greater part of the stomact has been removed by an incision made close to the pylorus. The transverse colon has been taken away and the small intestine has been cut across close to the duodeno-jejunal flexure.

A model prepared by the late Professor Birmingham has been made use of in this drawing.

lumbar vertebræ. In some cases, more frequently on the left side of the body, the eleventh rib also lies behind the upper part of the kidney. The relationship of the kidney to the lower two ribs is, however, very inconstant, owing partly to the great variability in size and inclination of these bones.

The inferior end of the kidney is usually situated from 1 to 2 inches above the highest part of the crest of the ilium; the interval between the kidney and the ilium being usually greater on the left side of the body.

Sometimes the inferior end of the kidney lies on the same level as, or only a short distance above, the iliac crest; this condition is sometimes due to the crest rising to a higher level than usual, the kidney occupying its normal position in relation to the vertebral column. It is important to remember that during life the kidney moves upwards and downwards, following the respiratory movements of the part of the diaphragm against which it rests.

The long axis of each kidney is somewhat oblique, its superior end approaching nearer to the median plane than the inferior. The surface of the kidney which is applied against the muscles forming the posterior wall of the abdomen looks,

as a whole, backwards and medially, and that which projects into the abdominal cavity looks forwards and laterally. Hence it happens that the lateral border lies on a more posterior plane than the medial border. The kidney is rotated in this manner on its long axis to such a degree that the medial margin and hilum are scarcely visible from behind, and only a limited view of the lateral border can be obtained from the front (Figs. 979 and 980).

The kidneys are placed behind the peritoneum, and project into the posterior part of the abdominal cavity. Each is surrounded by a considerable amount of loose tissue, often loaded with fat; the fatty tissue, or capsula adiposa, being present in greater quantity round the margins of the kidney, and only to a less extent in front of and behind the organ. The renal vessels and nerves lie in this fat before they enter the kidney, and the adipose tissue is continued, along with the vessels, through the hilum into the renal sinus, where it fills up all the space unoccupied by the vessels and nerves.

Embedded in the soft fatty tissue surrounding the kidney is a layer of fibrous

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FIG. 980.-TRANSVERSE SECTION THROUGH THE BODY OF A CHILD. The position and relationships of the kidneys are well seen, and the arrangement of the fascia renalis is indicated. The fascia is coloured green.

tissue to which the term fascia renalis is applied. This fascia surrounds the kidney and a considerable amount of its fatty capsule in the form of a loose sheath, in which may be distinguished anterior and posterior walls. The sheath is open inferiorly and medially, but closed above and to the lateral side of the kidney by the apposition of its walls. Laterally, the anterior and posterior walls of the sheath come into contact and are connected with the retro-peritoneal tissue. Medially they remain distinct, and the anterior wall is continued across the median plane, in front of the renal vessels and the aorta, to join the corresponding layer of the opposite side, while the posterior wall fuses with the fascia covering the psoas and quadratus lumborum muscles. Inferiorly, below the level of the kidney, the anterior and posterior layers of the renal fascia remain separate, and can be traced downwards into the iliac fossa. Above the level of the kidney and the suprarenal gland the layers of the renal fascia unite and join the fascia covering the diaphragm. It has been suggested that the terms "tunica adiposa" and "perinephric fat" should be restricted to the loose fatty tissue enclosed along with the kidney within the sheath of renal fascia, and that the term "paranephric body," or "fat," should be used to denote the tissue outside the sheath. The fibrous capsule of the kidney is joined to the loose sheath formed by

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)

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


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.

a. Depression corresponding to the transverse process of the first lumbar vertebra.

b. Depression corresponding to the transverse process of the second lumbar vertebra.
c. Depression corresponding to the twelfth rib.

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

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