530 



THE URINARY APPARATUS. 



[CH. XXXVI. 



in number from about 8 to 12, called calyces. Each of these 

 little calcyes or cups receives the pointed extremity or papilla of 

 a pyramid. The number of pyramids varies in different animals ; 

 in some there is only one. 



The kidney is a compound tubular gland, and both its cortical 

 and medullary portions are composed of tubes, the tuhuli uriniferi, 

 which, by one extremity, in the cortical portion, commence around 



tufts of capillary blood-vessels, 

 called Malpighian bodies, and, 

 by the other, open through 

 the papillae into the pelvis of 

 the kidney, and thus dis- 

 charge the urine which flows 



Fig. 415. Plan of a longitudinal section 

 through the pelvis and substance of the 

 right kidney, J : a, the cortical substance ; 

 6, b, broad part of the pyramids of Mal- 

 pighi ; c, c, the divisions of the pelvis 

 named calyces, laid open; </, one of those 

 unopened ; d, summit of the pyramids 

 of papillte projecting into calyces ; e, e, 

 section of the narrow part of two pyra- 

 mids near the calyces ; p, pelvis or en- 

 larged portion of the ureter within the 

 kidney ; u, the ureter ; s, the sinus ; 

 A, the hilus. 



Fig. 416. A. Portion of a secreting 

 tubule from the cortical sub- 

 stance of the kidney. B. The 

 epithelial or gland-cells, x 700 

 times. 



through them. They are bound together by connective-tissue. 



In the pyramids the tubes are straight uniting to form larger 

 tubes as they descend through these from the cortical portion; 

 while in the latter region they spread out more irregularly, and 

 become much convoluted. But in the boundary zone between 

 cortex and medulla, small collections of straight tubes called 

 medullary rays project into the cortical region. 



Tubuli Uriniferi. The tubuli uriniferi (fig. 420) are composed 

 of a basement membrane, lined internally by epithelium. They 

 vary considerably in size in different parts of their course, but 

 are, on an average, about ^^ of an inch (gVmm.) in diameter, 



