THE KIDNEYS. 



987 



by kidney-structure. Through this fissure the blood-vessels of the kidney and its 

 excretory duct pass, and therefore these structures, upon entering the kidney, are 

 contained within the sinus. The excretory duct, or ureter, after entering, dilates 

 into a wide, funnel-shaped sac named the pelvis. This divides into two or three 

 tubular divisions, which subdivide into several short, truncated branches named 

 calices or infwndibula, all of which are contained in the central cavity of the kid- 

 ney. The blood-vessels of the kidney, after passing through the hilum, are con- 

 tained in the sinus or central cavity, lying between its lining membrane and the 

 excretory apparatus, before entering the kidney-substance. 



This central cavity, as before mentioned, is surrounded on all sides except at 

 the hilum by the substance of the kidney, which is at once seen to consist of two 

 parts viz. of an external granular investing part, which is called the cortical 

 portion ; and of an internal part, the medullary portion, made up of a number of 

 dark-colored pyramidal masses, with their bases resting on the cortical part and 

 their apices converging toward the centre, where they form prominent papillae 

 which project into the interior of the calices. 



The cortical substance is of a bright reddish-brown color, soft, granular, and 

 easily lacerable. It is found everywhere immediately beneath the capsule, and is 

 seen to extend in an arched form over the base of each medullary pyramid. The 

 part separating the sides of any two pyramids through 

 which the arteries and nerves enter, and the veins and 

 lymphatics emerge, from the kidney, is called a cortical 

 column or column of Bertin (A, A', Fig. 543); while 

 that portion which stretches from one cortical column to 

 the next, and intervenes between the base of the pyra- 

 mid and the capsule (marked by the dotted line extend- 

 ing from A to A' in Fig. 543), is called a cortical arch, 

 the depth of which varies from a third to half an inch. 



The medullary substance, as before stated, is seen 

 to consist of red-colored, striated, conical masses, the 

 pyramids of Malpighi, the number of which, varying 

 from eight to eighteen, corresponds to the number of 

 lobes of which the organ in the foetal state is composed. 

 The base of each pyramid is surrounded by a cortical 

 arch, and directed toward the circumference of the kid- 

 ney ; the sides are contiguous with the cortical columns ; 

 while the apex, known as the papilla or mammilla of 

 the kidney, projects into one of the calices of the ureter, 

 each calyx receiving two or three papillae. 



These two parts, cortical and medullary, so dissimi- 

 lar in appearance, are very similar in structure, being 

 made up of urinary tubes and blood-vessels united and 

 bound together by a connecting matrix or stroma. 



Minute Anatomy. The tubuli uriniferi, of which 

 the kidney is for the most part made up, commence in 

 the cortical portion of the kidney, and, after pur- 

 suing a very circuitous course through the cortical and 

 medullary parts of the kidney, finally terminate at the 

 apices of the Malpighian pyramids by open mouths 

 (Fig. 544), so that the fluid which they contain is 

 emptied into the dilated extremity of the ureter con- 

 tained in the sinus of the kidney. If the surface of 

 one of the papillae is examined with a lens, it will be seen to be studded over with 

 a number of small depressions, from sixteen to twenty in number, and in a fresh 

 kidney, upon pressure being made, fluid will be seen to exude from these depres- 

 sions. They are the orifices of the tubuli uriniferi, which terminate in this situa- 

 tion. They commence in the cortical portion of the kidney as the Malpigliian 



FIG. 544. Plan of uriniferous 

 tubes. A, A. Malpighian bodies. 

 B, B. Margin of medullary struc- 

 ture, c, c, c. Loops of Henle. 



D. D, D. Straight tubes cut off. 



E. Commencing straight tubes. 



F. Termination of straight tube. 



