STRUCTURE OF THE KIDNEY. 



443 



dozen conical bundles of urine-tubes, 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 subdivided 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, again, receives the pointed extremity or 

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

 papilla is received by a calyx. 



The kidney is a gland of the class called tubular, and 

 both its cortical and medullary portions are composed 

 essentially of secreting tubes, the tubuli uriniferi, which by 

 one extremity, in the cortical Fit/. 114.*' 



portion, end commonly in little 

 saccules containing blood-ves- 

 sels, called Malpighian bodies, 

 and by the other open through 

 the papilla into the pelvis of the 

 kidney, and thus discharge the 

 urine which flows through them. 



In the pyramids they are 

 chiefly straight dividing and 

 diverging 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. 



The tubuli uriniferi (fig. 114) are composed of a nearly 

 homogeneous membrane, lined internally by spheroidal 

 epithelium, and for the greater part of their extent are 

 about ^-J-Q- of an inch in diameter, becoming somewhat 



* Fig. 114. A. Portion of a secreting canal from the cortical substance 

 of the kidney. P. The epithelium or gland-cells, more highly magnified 

 (700 times). 



