The Kidneys are about 4 inches long, 2 inches broad, and 1 inches thick, the right being shorter and thicker than the left, which, however, is the larger. On the anterior surface of each kidney there is a blunt projection, formed by the pressure of adjoining organs, which in the right kidney forms a transverse ridge, and in the left a blunt summit. The position of the kidney may be indicated on the posterior surface by four lines, two horizontal from the spines of the eleventh dorsal and third lumbar, giving the upper and lower limits, and two vertical, one 1 inch, and the other 3 inches from the vertebral spines, indicating the inner and outer limits. The hilum corresponds to the level of the first lumbar spine, and is 2 inches from the middle line on the right, and 1 on the left side. In front the lower limit of the kidneys does not extend below the level of the umbilicus, corresponding generally to the lowest limit of the thoracic framework, and the hilum is about a finger-breadth inside the tip of the ninth costal cartilage. The right kidney lies inch lower than the left, its lower border being 1 inches from the iliac crest. The kidneys normally move with respiration, and when this movement is excessive, the kidney can frequently be palpated by one hand in front, and the other pressing forwards in the loin when the patient takes a long breath. While the kidney rarely ascends above its normal position, it is frequently found below it. This in some cases may be due to a congenital defect, the kidney normally ascending during foetal life from the pelvis into its normal position. In such cases the kidney is generally fixed in the abnormal position, and its vessels are short. Other congenital deformities are horseshoe kidney, absence of one kidney, or presence of a supernumerary kidney.

A downward displacement of one kidney, and particularly the right, frequently occurs, the condition being known as movable kidney. Normally, the kidney is kept in position by (1) the pressure of the abdominal wall exerted on it through the viscera, in conjunction with the peculiar shape of its anterior surface already referred to ; (2) its vessels ; (3) the attachments of the renal fascia, kept tense by the fat of the adipose capsule. If the adipose tissue be diminished, these attachments become slack, and so undue mobility is allowed. In such cases great latitude of movement may be possible, the kidney frequently being found in the pelvis, and gastric dilatation and transient jaundice may be produced by the traction of the kidney upon the duodenum. Floating kidney is the term applied to a similar but rare condition where the kidney possesses a mesonephron. As a rule, even where the kidney is very movable, its covering is composed of loose fibrous tissue derived from its capsule, and not peritoneum. The condition is most frequently met with in women, being predisposed to by pregnancy, causing relaxation of the abdominal parietes.

The inner borders of the kidneys look inwards and also forwards, and the lower extremities are wider apart, and are directed more forward than the upper extremities. The kidneys lie behind the peritoneum, which is only closely related to the outer border, the anterior surface being embedded in the extraperitoneal fat, which in this region is very abundant, constituting the capsula adiposa of the kidney. This in turn is surrounded by a fibrous investment, the fascia renalis, also composed of extraperitoneal tissue, which ,splits into two layers to enclose the kidney, fatty envelope, suprarenal capsule, renal vessels, and commencement of the ureter. This fascia is attached above and externally to the diaphragm, and then splits to enclose the kidney, the anterior layer passing in front of the kidney, its vessels, and the aorta, and becoming continuous with that of the opposite side, while the posterior layer passes behind the kidney, and is attached to the front of the spine along the inner border of the psoas. Below the level of the kidney the two layers continue separately in the direction of the iliac fossa, and are gradually lost. This renal fascia sends in numerous trabecular, which, traversing the adipose layer, fuse with the proper capsule of the kidney.

The proper capsule of the kidney is tough and fibrous, but normally is not very adherent to the kidney substance. It plays an important part in limiting effusions within the kidney substance, may practically form the cyst wall in advanced hydronephrosis, and is utilized in the operation of nephrorrhaphy.

Posteriorly, the kidneys are in relation to the diaphragm, internal and external arcuate ligaments, fascia of the psoas and quadratus lumborum and lumbar fascia, the twelfth rib which crosses obliquely at the junction of the upper and middle one-third, and transverse processes of the two upper lumbar vertebrae. Externally, the right kidney is in relation to the liver, and the left to the spleen. In front, the right kidney is related to the under surface of the liver, ascending and commencement of transverse colon, and second part of duodenum ; the left to the fundus of the stomach, descending colon, and pancreas.

The relationship to the twelfth rib is of importance, as the reflection of the parietal pleura from diaphragm to chest wall takes place about this level, and sometimes even below it, and maintains this level even when the twelfth rib is rudimentary. It is therefore wise, before commencing a lumbar operation on the kidney, to count the ribs and commence the incision fully inch below the lower border of the twelfth rib.

The renal artery arises from the aorta at the level of the first lumbar vertebra. The right is larger than the left, and passes under the vena cava. The artery divides into several large branches before entering the kidney. The small vessels within the kidney substance pursue a pretty straight course, and, as they are practically end arteries, infarctions not infrequently occur in the kidney substance.

The renal veins empty into the inferior vena cava, the left being longer and crossing in front of the aorta, while the left spermatic vein opens into it at right angles. The renal veins lie in front of the arteries, which in turn are in front of the ureters.

The nerves are derived from the renal plexus (from the solar) and accompanying branches of the artery. The segments of the cord involved are from the tenth dorsal to first lumbar, through the small and lesser splanchnics, and hi renal affections pain (e.g., dragging pain in movable kidney)'is referred along the sensory nerves derived from these segments.

The expanded pelvis of the kidney, which is situated partly within the lips of the hilum and partly beyond, presents several depressions, or calyces, on which the papillae open. The renal pelvis on the right side is related to the duodenum in front, and vena cava on its inner border ; on the left to the body of the pancreas and jejunum in front, and aorta some distance from its inner border.

Infection may reach the kidney by the blood-stream, producing multiple small cortical abscesses, or most commonly by the ureter. In the latter case the infection generally extends up from the bladder, producing a pyelitis, and by further extension suppurative foci in the kidney substance (so called ' surgical kidney '). Once the ureter becomes blocked, a pyonephrosis occurs. An abscess in the tissue surrounding the kidney (perinephric abscess) may arise by extension from the kidney or from suppurative appendicitis, empyema perforating the diaphragm, etc. Such abscesses generally point about Petit's triangle, but, owing to the laxness of the tissues, may spread widely in the extraperitoneal tissues before pointing externally, sometimes descending into the iliac fossa or opening into the colon or rectum. The kidney is frequently affected by tubercle (through the bloodstream). Calculi, particularly uric acid or oxalates, form about the renal pelvis, and, if movable, may cause renal colic when attempting to descend the ureter.

Injuries to the kidneys generally result from severe crushes, the kidney being lacerated by pressure against the last rib, or transverse processes and bodies of the two upper lumbar vertebrae. Where the capsule is ruptured, a large extravasation of blood and urine may take place into the extraperitoneal tissues. Ruptures of the kidney are more frequently recovered from than similar injuries of the other viscera, owing to their extraperitoneal position. Hematuria frequently follows injuries to the back, owing to the kidney being crushed between the ilium and lower ribs in acute anterior flexion.

Operations-Nephrotomy (incision into). Nephrolithotomy (incision for the removal of stone), Nephrectomy (removal),