THE KIDNEYS. 



1131 



centre of the group are the longest, and reach almost to the surface of the kidney, 

 while the external ones are shorter, and advance only a short distance into the 



.... , Curved 

 Dutal collecting 

 cmivo- 



luted 

 tubule. 

 I 



Descending limb \ 

 of Henle' sloop, j 



FIG. 720. Uriniferons tube. For the sake of clearness the epithelial cells have been represented more 

 highly magnified than the tubes in which they are contained, 



cortex. In consequence of this arrangement the cortical portion presents a number 

 of conical masses, the apices of which reach the periphery of the organ, and the 

 bases are applied to the medullary portion. These are termed the pyramids of 

 F-rrein. As they run through the cortical portion the straight tubes receive on 

 either side the curved extremity of the convoluted tubes, which, as stated above, 

 commence at the Malpighian bodies. The portions of the cortex between the 

 medullary rays are known as the labyrinth of the cortex. 



It will be seen from the above description that there is a continuous series 

 of tubes from their commencement in the Malpighian bodies to their termina- 

 tion at the orifices on the apices of the pyramids of Malpighi, and that the 

 urine, the secretion of which commences in the capsule, finds its way through 

 these tubes into the calices of the kidney, and so into the ureter. To recapitulate : 

 the tube first presents a constricted portion, (1) the neck. 2. It forms a wide 

 convoluted tube, the proximal convoluted tube. 3. It becomes spiral, the spiral 

 tubule "f Sekaehowa. 4. It enters the medullary structure as a narrow, straight 

 tube, the descending limb of Henle s loop. 5. Forming a loop and becoming 

 dilated, it ascends somewhat spirally, and. gradually diminishing in calibre, 

 again enters the cortical structure, the ascending limb of Henle' s loop. 6. It now 

 becomes irregular and angular in outline, the irregular tubule. 7. It then becomes 

 convoluted, the distal convoluted tubule. 8. Diminishing in size, it forms a curve, 

 the curved tubule. 9. Finally, it joins a straight tube, the straight collecting tube,, 

 which is continued downward through the medullary substance to open at the apex 

 of a pyramid. 



The Tubuli Uriniferi: their Structure. The tubuli uriniferi consist of base- 



