STRUCTURE OP THE KIDNEY 



369 



the cortex, and is the darker and more compact of the two. 

 The inner layer is called the medulla. This medullary 

 substance is less red than the cortex, and is divided into 

 pyramids whose small ends are toward the pelvis and 

 whose bases are toward the cortex. These pyramids are 

 called the pyramids of Malpighi. 



The renal artery divides in the hilus (the name given to 

 the depression), and its branches extend between the pyra- 

 mids to the cortex. While they 

 give off a few branches to the 

 pyramids they end in a much 

 richer network of capillaries in 

 the cortex, and to this fact is due 

 the deeper color of the cortex. 

 These cortex capillaries are in 

 turn collected into veins which 

 ultimately empty into the common 

 renal vein, foUovring a path similar 

 to that of the arteries through the 

 kidneys. 



The pjTamids of the medullary 

 layer are composed of fine tubular 

 glands. At the points of the 

 pyramids are found opening into 

 the calices the mouths (the papillae) 

 of many tiny tubes (the urini- 

 ferous tubules). These tubules 

 extend backward into the med- 

 ullary layer, branching frequently, 

 and thus forming the pyramid. 

 Ultimately these branches end in the cortex, where they 

 swell but and form a spherical capsule (Malpighian capsule.) 



EDDY. PHYS. 24 



Fig. 170 — A uriniferous tu- 

 bule; r, cortical portion of 

 kidney; g^ medullary por- 

 tion; p, a pyramid; /, a Mal- 

 pighian capsule; // and V, 

 twisted portions of tubule; 

 ///, IV, VI- VIII, straight 

 portions of tubule; tX, open- 

 ing of tubule into pelvis at 

 top of pyramid. 



