180 ' STUDENTS HISTOLOGY 



1. The capsule of the kidney. 



2. The ureter. 



3. The pelvis, with its three infundibula. The subdivision of 

 each infundibulum into several calyces. Each calyx the site of the 

 apex of a Malpighian pyramid. 



4. The Mood -vessels entering and leaving the hilum. Their 

 subdivision outside the pelvic lining, and final passage into the 

 kidney -substance in the cortical columns. 



5. Division of kidney -substance into cortex and medullary or 

 Malpighian pyramids. 



6. Penetration of cortical tissue inward between pyramids of 

 Malpighi constituting the cortical columns. 



7. The pyramids of Ferrein. 



8. The labyrinths. 



In the domestic animals there are no cortical columns the 

 pyramids of Malpighi coalescing, as it were thus presenting a 

 true medulla. 



We have remarked that the kidney is made up largely of urine- 

 carrying vessels (the tubuli uriniferi) and blood-vessels. We will 

 first study the tubular system, reserving for the present the con- 

 sideration of the blood-vessel arrangement. 



THE TUBULI URINIFERI 



The urine -carrying tubules commence in the cortex, and, after 

 taking a very circuitous route with frequently varying diameters, 

 end at the apex of the pyramids of Malpighi, where they pour 

 their contained urine into the calyces. The urine then overflows 

 into the infundibula, and is finally drained from the pelvis by 

 the ureter. 



We shall begin with a single typical tube ; and, understanding 

 its histology, we can build up the organ by simply multiplying 

 this element. 



A uriniferous tube, or tubule, commences in the cortex in the 

 labyrinth (between the pyramids of Ferrein), as a thin -walled sac 

 .2 mm. in diameter. This vesicle, with its contents, is a Mal- 

 pighian body ; and its wall is called the capsule of the same, or 

 the ca2)sule of Bowman. The capsule consists of a thin layer of 

 connective tissue lined by flat epithelial cells. 



From one side of this, the expanded beginning of the tube, a 

 narrow neck (25 p* in diameter) is projected, which immediately 



