THE KIDNEYS 



1221 



of the kidney be made from its convex to its concave border, it will be seen that the 

 hilum expands into a central cavity, the renal sinus, this contains the upper part of 

 the renal pelvis and the calyces, surrounded by some fat in which are imbedded the 

 branches of the renal vessels and nerves. The renal sinus is lined by a prolongation 

 of the fibrous tunic, which is continued around the lips of the hilum. The renal 

 calyces, from seven to thirteen in number, are cup-shaped tubes, each of which 

 embraces one or more of the renal papilla?; they unite to form two or three short 

 tubes, and these in turn join to form a funnel-shaped sac, the renal pelvis. The 

 renal pelvis, wide above and narrow below where it joins the ureter, is partly out- 

 side the renal sinus. The renal calyces and pelvis form the upper expanded end of 

 the excretory duct of the kidney. 



The kidney is composed of an internal medullary and an external cortical substance. 



The medullary substance (substantia medullaris] consists of a series of red-colored 

 striated conical masses, termed the renal pyramids, the bases of which are directed 

 toward the circumference of the kidney, while their apices converge toward the 

 renal sinus, where they form prominent papillae projecting into the interior of the 

 calyces. 



The cortical substance (substantia corticalis) is reddish brown in color and soft and 

 granular in consistence. It lies immediately beneath the fibrous tunic, arches over 

 the bases of the pyramids, and dips in between 

 adjacent pyramids toward the renal sinus. The 

 parts dipping in between the pyramids are 

 named the renal columns (Bertini), while the 

 portions which connect the renal columns to 

 each other and intervene between the bases of 

 the pyramids and the fibrous tunic are called 

 the cortical arches (indicated between A and A' 

 in Fig. 1127). If the cortex be examined with a 

 lens, it will be seen to consist of a series of 

 lighter-colored, conical areas, termed the radiate 

 part, and a darker-colored intervening substance, 

 which from the complexity of its structure is 

 named the convoluted part. The rays gradually 

 taper toward the circumference of the kidney, 

 and consist of a series of outward prolongations 

 from the base of each renal pyramid. 



Minute Anatomy. The renal tubules (Fig. 1028), 

 of which the kidney ia for the most part made up, 

 commence in the cortical substance, and after pursuing 

 a very circuitous course through the cortical and medul- 

 lary substances, finally end at the apices of the renal 

 pyramids by open mouths, so that the fluid which 

 they contain is emptied, through the calyces, into the 

 pelvis of the kidney. If the surface of one of the 

 papillae be examined with a lens, it will be seen to be 



studded over with minute openings, the orifices of the renal tubules, from sixteen to twenty 

 in number, and if pressure be made on a fresh kidney, urine will be seen to exude from these 

 orifices. The tubules commence in the .convoluted part and renal columns as the renal cor- 

 puscles, which are small rounded masses of a deep red color, varying in size, but of an average 

 of about 0.2 mm. in diameter. Each of these little bodies is composed of two parts: a central 

 glomerulus of vessels, and a membranous envelope, the glomerular capsule (capsule of Bowman), 

 which is the small pouch-like commencement of a renal tubule. 



The glomerulus is a lobulated net-work of convoluted capillary bloodvessels, held together 

 by scanty connective tissue. This capillary net-work is derived from a small arterial twig, 

 the afferent vessel, which enters the capsule, generally at a point opposite to that at which 

 the latter is connected with the tubule; and the resulting vein, the efferent vessel, emerges 

 from the capsule at the same point. The afferent vessel is usually the larger of the two 



FIG. 1127. Vertical section of kidney. 



