348 



HAND-BOOK OF PHYSIOLOGY. 



On making a section lengthwise through the kidney (Fig. 238) the 

 main part of its substance is seen to be composed of two chief portions, 

 called respectively the cortical and the medullary portion, the latter being 

 also sometimes called the pyramidal portion, from the fact of its being 

 composed of about a dozen conical bundles of urine-tube, each bundle 

 being called a pyramid. The upper part of the duct of the organ, or the 

 ureter, is dilated into what is called the pelvis of the kidney; and this, 

 again, after separating into two or three principal divisions, is finally sub- 

 divided into still smaller portions, varying in number from about 8 to 12, 

 or even more, and called calyces. Each of these little calyces or cups, 

 which are often arranged in a double row, receives the pointed extremity 

 or papilla of a pyramid. Sometimes, however, more than one papilla is 

 received by a calyx. 



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

 medullary portions are composed essentially of secreting tubes, the tuliili 

 uriniferi, which, by one extremity, in the cortical portion, end commonly 

 in little saccules containing blood-vessels, called Malpigliian bodies, and, 

 by the other, open through the papillae into the pelvis of the kidney, and 

 thus discharge the urine which flows through them. 



FIG. 239. A. Portion of a secreting tubule from the cortical substance of the kidnej'. B. The epi- 

 thelial or gland-cells. X 700 times. 



In the pyramids the tubes are chiefly straight dividing and diverg- 

 ing as they ascend through these into the cortical portion; while in the 

 latter region they spread out more irregularly, and become much branched 

 and convoluted. 



Tubuli Uriniferi. The tubuli uriniferi (Fig. 239) are composed of 

 a nearly homogeneous membrane, and are lined internally by epithelium. 

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

 on an average, about -g-}-^ of an inch in diameter, and are found to be 



