THE KIDNEYS. 1267 



tissue, which completely surrounds each tubule and blood-vessel, and binds it to its 

 neighbours. It has been found possible to obtain an accurate idea of the arrangement of 

 this connective tissue by submitting thin sections of the kidney to the action of certain 

 digestive fluids. When this is done the tubules and blood-vessels are removed, and the 

 connective tissue stroma is left behind. The connective tissue thus revealed is seen to 

 form a continuous network, the spaces in which faithfully reproduce the outlines and 

 the arrangement of the kidney tubules. The network of the stroma is continuous with 

 the capsule of the kidney. 



Vessels of the Kidney. The renal artery comes directly from the aorta, and is 

 very large in proportion to the size of the organ to which it conveys blood. Its main 

 branches, as they approach the kidney to enter the hilum, lie between the tributaries of 

 the renal vein in front and the ureter behind. Within the sinus of the kidney the 

 branches of the renal artery become arranged in a dorsal and a ventral group, the dorsal 

 vessels lying behind, the ventral ones in front of the subdivisions of the ureter. The 

 ventral group of vessels supplies the part of the kidney which forms the anterior and 

 lateral walls of the sinus; the distribution of the dorsal group is for the most part 

 restricted to the portion of the kidney which lies behind, and to the medial side of 

 the sinus. 



Entering the substance of the kidney in the manner described above (p. 1265), the larger 

 arteries lie in the intervals between the pyramids, and are called the arterise interlobares 

 renis or interlobar arteries. These vessels dividing, form a series of incomplete arterial 

 arches, the arteriae arciformes, which pass across the bases of the pyramids. Although 

 we speak of arterial arches, it must be understood that no anastomosis between the 

 branches of the interlobar arteries actually takes place, but that each artery which 

 enters the wall of the kidney sinus has an isolated distribution and possesses the 

 characters of an "end artery." Each arterial arch gives off a number of vessels which 

 pass through the convoluted part of the cortex towards the surface of the kidney. These 

 are known as the arteriae interlobulares, and lie at very regular intervals. From them a 

 number of short branches arise, termed vasa afferentia, each of which proceeds to the 

 dilated extremity, or capsule, of a uriniferous tubule. Here the vas afferens breaks up 

 into a much convoluted capillary mass, called a glomerulus, which is contained within the 

 invagination of the capsule. The little vein which issues from the glomerulus, or vas 

 efferens, instead of running directly into a larger vein, breaks up, after the manner of 

 an artery, into capillaries which supply the tubules of the convoluted and radiate parts 

 of the kidney cortex. Hence almost all the blood which supplies the tubules of 'the 

 cortical part of the kidney passes in the first instance through the glomeruli. The tubules 

 of the bases of the pyramids also receive their blood-supply through vasa efferentia derived 

 from the glomeruli which lie near. The little vessels passing from these glomeruli break 

 up into bundles of fine arteries, which give the bases of the pyramids their coarsely 

 striated appearance. They are known as arteriolae rectae, and, like the arterise inter- 

 lobulares, are very conspicuous in injected preparations of the kidney. 



The fibrous capsule of the kidney receives minute branches from the interlobular 

 arteries, some of which, piercing the capsule, communicate by capillaries with the vessels of 

 the tunica adiposa. 



Veins corresponding to the interlobular arteries and arteriolse rectse collect the blood 

 from the capillaries surrounding the tubules, and unite to form a series of complete arches 

 across the bases of the pyramids. From these venous arcades vessels arise, which traverse 

 the intervals between the pyramids and reach the sinus of the kidney, where they unite 

 to form the dorsal and ventral tributaries of the renal vein. Some small veins in the 

 superficial part of the cortex communicate through the fibrous capsule with minute veins 

 in the capsula adiposa. Issuing from the kidney sinus, the veins run a direct course to 

 end in the inferior vena cava. 



Nerves of the Kidney. The nerves of the kidney accompany the branches of the 

 artery, and are derived from the renal plexus. Their minute branches form regular 

 net-like plexuses on the walls of the fine arteries and kidney tubules, and the presence of 

 nerve terminations occurring among the epithelial cells lining the tubules has within 

 recent years been demonstrated. 



From clinical evidence it would appear that the nerve fibres which supply the kidney 

 are portions of the tenth, eleventh, and twelfth thoracic nerves. 



Variations. A marked difference in the size of the two kidneys is sometimes observed, 

 a small kidney on one side of the body being usually compensated for by a large kidney on the 

 opposite side. Cases of complete absence of one or other kidney are recorded. 



A few cases are on record in which an extra kidney was found on the right or left side. 



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