MINUTE STRUCTURE OF THE KIDNEY. 265 



apex of the pyramid, which projects, as the papilla, into a 

 calyx of the ureter. At its outer end each pyramid separates 

 into smaller portions, 2", separated by thin layers of cortex 

 and gradually spreading everywhere into the latter. The 

 cortical substance is redder, more granular looking, and 

 less shiny than the medullary; it forms everywhere the 

 outer layer of the organ, besides dipping in between the 

 pyramids in the manner above described. 



The renal artery divides in the hilus into branches (5) 

 which run into the kidney substance between the pyra- 

 mids, give off a few twigs to the pyramids, and end finally 

 in a much closer vascular network in the cortex. 



The Minute Structure of the Kidney. The kidneys are 

 compound tubular glands, being composed of branched 

 microscopic uriniferous tubules, lined by a single layer of 

 secreting cells, supported by connective tissue, and supplied 

 with blood-vessels, nerves, and lymphatics. The final 

 branches of each tubule end in a dilatation which contains 

 a knot of blood-vessels, through whose walls water and 

 salts filter into the tubule. As the water trickles along the 

 latter, the cells lining it pass out the nitrogenous wastes 

 of the blood brought there by the capillaries which wrap 

 closely around them. The tubules unite in the pyramids 

 to form fewer and larger ducts, which pour the secretion 



How does the apex of a pyramid end? Where do we find the cor- 

 tical substance of the kidney? 



Describe the general distribution of the renal artery and its 

 branches in the kidney. Wliat part of the kidney contains most 

 capillary biood- vessels? 



To what type of gland do the kidneys belong? Of what are they 

 'made up? How do the uriniferous tubules end? What lies in each 

 dilatation? What niters from the blood-vessels of its dilatation into 

 the cavity of the tubule? What is added to this as it trickles along 

 the tubule? How is the nitrogenous waste of the body brought close 

 to the kidney tubules? What becomes of the tubules in the pyra- 

 mids? Where do the larger ducts convey the secretion? 



