770 SPECIAL PHYSIOLOGY. 



lary portion, which is disposed in a series of conical masses. The 

 cortical substance is about 2 lines in thickness, and forms about { of 

 the entire gland. It is of a reddish color, soft, granular, and friable, 

 and contains a number of little round dark-red spots, which indicate 

 the position of certain minute bodies, named the Malpighian cor- 

 puscles of the kidney. The conical masses of the medullary substance, 

 from fifteen to twenty in number, form the so-called pyramids (Mal- 

 pighi). Their bases, turned towards the surface of the kidneys, and 

 also their sides, are encompassed by the cortical substance ; but their 

 apices are turned towards the sinus, in the interior of the organ, 

 where they form little eminences, called the papillce or mammilla?. 

 The substance of the pyramids is firmer and darker than the cortical 

 substance, and, as seen on a section, is striated from apex to base, the 

 latter part being much darker than the former. 



Outside the hilus, the ureter presents a funnel-shaped dilatation, or 

 membranous cavity, called the pelvis of the kidney, which, as it passes 

 into the sinus, divides into three tubes, named the infundibula; these 

 again subdivide into from seven to thirteen smaller, also funnel-shaped, 

 tubes, called the calyces, which surround, or embrace, the papillae. 

 One calyx often includes two, or even three, papillae, so that they are 

 usually fewer in number than the latter. 



The cortical and medullary substances are both composed of minute 

 closely packed tubules or ducts, the tubuli uriniferi, with bloodvessels, 

 absorbents, and nerves, held together by a soft material of ill defined 

 structure. The latter is described as consisting of a very fine, scarcely 

 recognizable, areolar tissue or stroma, more evident in the medullary 

 portion, but forming, at the surface of the kidney, a thin layer be- 

 neath the fibrous coat ; a parenchyma is also described by some. The 

 different appearance of the cortical and medullary substances, depends 

 on the different arrangement of their ducts and bloodvessels. 



In the cortical portion the tubuli uriniferi are very numerous, much 

 convoluted, and inosculate freely with each other; they are, on an 

 average, about gj^th of an inch in diameter, and are known as the 

 tubes of Ferrein. They generally commence by free closed extremi- 

 ties; sometimes, however, they anastomose together, forming loops; 

 many are said to begin as minute purse-like dilatations, which form 

 little partial capsules around the Malpighian corpuscles (Bowman) ; 

 nearly all are somewhere connected with these capsules. In the pyra- 

 mids, or medullary substance, the tubuli quickly unite together many 

 times, dichotomously or by twos, and becoming larger and straight, 

 constitute the so-called ducts of Bellini; these form tapering bundles, 

 directed to the papillae, or apices, of the pyramids, on which they open 

 by minute round orifices. It has been estimated that there are as many 

 as two millions of tubuli in each kidney; that the number of orifices 

 in a square line of a papilla, are 100; and that there are from 300 to 

 500 on the surface of a single papilla. (Krause.) The straight tubuli 

 are widest near their orifices, measuring from 2 J^th to 4 J^th of an 

 inch ; they cause the striated appearance of the pyramids. The urin- 

 iferous tubules are composed of a transparent basement membrane, 

 lined with a thick polygonal, or spheroidal, glandular epithelium, 



