THE KIDNEYS AND THE URINE. 



75 



Malpighian Body. 



capillaries which are surrounded by a capsule lined by epithelial 

 cells (Fig. 18). and here it it is that the urin- 

 iferous tubules arise, the tuft of capillary FIG. 18. 

 vessels being, as it were, built into the end 

 of the tubule. 



What are the uriniferous tubules? 



Beginning in the cortex of the kidney at 

 one of the bodies of Malpighi, the minute 

 secreting ducts pursue a tortuous course to 

 the larger collecting tubules, which empty at 

 the apices of the pyramids of Malpighi into 

 the calyces of the kidney. Without entering 

 minutely upon the course of the tubules, it is 

 important to remember that they form a loop 

 (of Henle) which dips into the pyramid, and 

 that they pursue a somewhat tortuous course 

 both before entering into the loop of Henle 

 and upon returning to the cortical portion of 

 the kidney, where they empty into the straight collecting tubules. 

 The straight course of the arms of Henle's loop and of the collect- 

 ing tubules gives to the pyramids a finely striated apppearance. 

 (See Fig. 19.) 



Describe the blood-circulation in the kidney. 



On entering the kidney the renal artery breaks up into several 

 branches, which pass into the tissue proper of the organ. Branches 

 from these arteries (arteria propria renales) have two determina- 

 tions (1) into the cortex, and (2) into the pyramids. 



(1) Those branches (interlobular) which pass into the cortex 

 divide to become the afferent vessels to the Malpighian bodies, and, 

 after there passing through the capillary tuft, the blood is re-col- 

 lected and goes out by an efferent vessel. This efferent vessel in 

 its turn is broken into a minute capillary plexus which surrounds 

 the uriniferous tubules in the cortex of the kidney, and these 

 capillaries unite to form the venous return circulation. Thus, this 

 system has, it is to be noted, tico capillary divisions, in the Malpighian 

 tuft, and again about the tubules of the cortex. 



(2) Numerous minute branches (arterise rectae) are given off, 

 which pass into the pyramids, surround the portion of the urin- 

 iferous tubule (Henle's loop) which passes into the medullary 



