THE KIDNEYS. 



1129 



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. 716) ; whilst that portion which 

 stretches from one cortical column to the next, and intervenes between the base of 

 the pyramid and the capsule (marked by the dotted line from A to A' in Fig. 716), 

 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 pale red- 

 colored, striated, conical masses, the pyramids of Malpighi, the number of which, 

 varying from eight to eighteen, correspond 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 kidney ; the sides 

 are contiguous with the cortical columns ; whilst the apex, known as the papilla 

 or ma/iuinUa of the kidney, projects into one of the 

 calices of the ureter, one calyx receiving two or three 

 papillae. 



These two parts, cortical and medullary, so dissimilar 

 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 pursuing 

 a very circuitous course through the cortical and med- 

 ullary parts of the kidney, finally terminate at the 

 anices of the Malpighian pyramids by open mouths 

 (Fig. 717), 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 depres- 

 sions from sixteen to twenty in number, and in a fresh 

 kidney, upon pressure being made, fluid will be seen to 

 exude from these depressions. They are the orifices of 

 the tubuli uriniferi. which terminate in this situation. 

 They commence in the cortical portion of the kidney 

 as the Malpighian bodies, which are small rounded 

 masses, varying in size, but of an average of about 

 y|-ij of an inch in diameter. They are of a deep-red 

 color, and are found only in the cortical portion of the 

 kidney. Each of these little bodies is composed of two 

 parts a central glomerulus of vessels, called a Mal- 

 pighian tuft, and a membranous envelope, the Mal- 

 [>i</]ii<in capsule, or capsule of Bowman, which latter is 

 a small pouch-like commencement of a uriniferous tubule. 



The Malpighian tuft, or vascular glomerulus, is a network of convoluted 

 capillary blood-vessels held together by scanty connective tissue and grouped into 

 from two to five lobules. This capillary network is derived from a small arterial 

 twig, the afferent vessel, which pierces the wall of the capsule, generally at a point 

 opposite that at which the latter is connected with the tube ; 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. 718). The Malpighian or Bowman s 

 capsule, which surrounds the glomerulus, is formed of a hyaline membrane sup- 

 ported by a small amount of connective tissue which is continuous with the con- 

 nective tissue of the tube. It is lined on its inner surface by a layer of squa- 



FIG. 717. A, A. Malpighian 

 bodies. B,B. Margin of medullary 

 structure, c, c, c. Loops of Henle. 

 D, D, D. Straight tubes cut off. E. 

 Commencing straight tubes. F. 

 Termination of straight tube. 



