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Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
 
  The venæ rectæ are branches from the plexuses at the apices of the medullary pyramids, formed by the terminations of the arteriæ rectæ. They run outward in a straight course between the tubes of the medullary substance, and joining, as above stated, the interlobular veins, form venous arcades; these in turn unite and form veins which pass along the sides of the pyramids (Fig. 1128).
  These vessels, venæ propriæ renales, accompany the arteries of the same name, running along the entire length of the sides of the pyramids, and quit the kidney substance to enter the sinus. In this cavity they join the corresponding veins from the other pyramids to form the renal vein, which emerges from the kidney at the hilum and opens into the inferior vena cava; the left vein is longer than the right, and crosses in front of the abdominal aorta.
  The lymphatics of the kidney are described on page 712.

Nerves of the Kidney.—The nerves of the kidney, although small, are about fifteen in number. They have small ganglia developed upon them, and are derived from the renal plexus, which is formed by branches from the celiac plexus, the lower and outer part of the celiac ganglion and aortic plexus, and from the lesser and lowest splanchnic nerves. They communicate with the spermatic plexus, a circumstance which may explain the occurrence of pain in the testis in affections of the kidney. They accompany the renal artery and its branches, and are distributed to the bloodvessels and to the cells of the urinary tubules.

Connective Tissue (intertubular stroma).—Although the tubules and vessels are closely packed, a small amount of connective tissue, continuous with the fibrous tunic, binds them firmly together and supports the bloodvessels, lymphatics, and nerves.

Variations.—Malformations of the kidney are not uncommon. There may be an entire absence of one kidney, but, according to Morris, the number of these cases is “excessively small”: or there may be congenital atrophy of one kidney, when the kidney is very small, but usually healthy in structure. These cases are of great importance, and must be duly taken into account when nephrectomy is contemplated. A more common malformation is where the two kidneys are fused together. They may be joined together only at their lower ends by means of a thick mass of renal tissue, so as to form a horseshoe-shaped body, or they may be completely united, forming a disk-like kidney, from which two ureters descend into the bladder. These fused kidneys are generally situated in the middle line of the abdomen, but may be misplaced as well. In some mammals, e. g., ox and bear, the kidney consists of a number of distinct lobules; this lobulated condition is characteristic of the kidney of the human fetus, and traces of it may persist in the adult. Sometimes the pelvis is duplicated, while a double ureter is not very uncommon. In some rare instances a third kidney may be present.
  One or both kidneys may be misplaced as a congenital condition, and remain fixed in this abnormal position. They are then very often misshapen. They may be situated higher, though this is very uncommon, or lower than normal or removed farther from the vertebral column than usual; or they may be displaced into the iliac fossa, over the sacroiliac joint, on to the promontory of the sacrum, or into the pelvis between the rectum and bladder or by the side of the uterus. In these latter cases they may give rise to very serious trouble. The kidney may also be misplaced as a congenital condition, but may not be fixed; it is then known as a floating kidney. It is believed to be due to the fact that the kidney is completely enveloped by peritoneum which then passes backward to the vertebral column as a double layer, forming a mesonephron which permits movement. The kidney may also be misplaced as an acquired condition; in these cases the kidney is mobile in the tissues by which it is surrounded, moving with the capsule in the perinephric tissues. This condition is known as movable kidney, and is more common in the female than in the male. It occurs in badly nourished people, or in those who have become emaciated from any cause. It must not be confounded with the floating kidney, which is a congenital condition due to the development of a mesonephron. The two conditions cannot, however, be distinguished until the abdomen is opened or the kidney explored from the loin.
 
3b. 2. The Ureters
 
  The ureters are the two tubes which convey the urine from the kidneys to the urinary bladder. Each commences within the sinus of the corresponding kidney as a number of short cup-shaped tubes, termed calyces, which encircle the renal papillæ. Since a single calyx may enclose more than one papilla the calyces are generally fewer in number than the pyramids—the former varying from seven to thirteen, the latter from eight to eighteen. The calyces join to form two or three short tubes, and these unite to form a funnel-shaped dilatation, wide above and narrow below, named the renal pelvis, which is situated partly inside and partly outside the renal sinus. It is usually placed on a level with the spinous process of the first lumbar vertebra.

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