EXCRETION. 



through its long convex border (fig. 287), the main part of its substance 

 is seen to be composed of two chief portions called respectively cortical 

 and medullary, the latter being also sometimes called pyramidal, from 

 the fact of its being composed of about a dozen conical bundles of urine 

 tubes, each bundle forming what is called a pyramid. The upper part 

 of the ureter or duct of the organ, is dilated into the pelvis ; 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, which are often arranged in a double row, receives the pointed 



Fig. 287. Fig. 288 



Fig. 287. Plan of a longitudinal section through the pelvis and substance of the right kidney 

 Jt 5 , the cortical substance : 6, 6, broad part of the pyramids of Malpighi; e, c, the divisions of the 

 pelvis named calyces, laid open ; c', one of those unopened ; d, summit of the pyramids of papillae 

 projecting into calyces ; e, e, section of the narrow part of two pyramids near the calyces; p, pel- 

 vis or enlarged divisions of the ureter within the kidney; u, the ureter; s, the sinus; h, the hilus. 



Fig. 288. A. Portion of a secreting tubule from the cortical substance of the kidney. B. The epi- 

 thelial or gland- cells. X 700 times. 



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 tubes, the tubuli urini- 

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

 little saccules containing blood-vessels, called Malpighian bodies, and, 

 by the other, opened through the papillae into the pelvis of the kidney, 

 and thus discharge the urine which flows through them. 



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. 288) are composed of 



