SECRETION. 439 



The collecting tubes, as they run toward the medulla of the kid- 

 ney, unite with other distal convoluted tubules. They also unite at 

 acute angles with adjacent collecting tubes finally to pass to the 

 papilla?. The loops of Henle and the collecting tubes constitute the 

 tiibuli recti. Each uriniferous tubule is thus completely isolated as 

 far as the junction of the distal contorted tubes with the collect- 

 ing tube. 



A portion of the loops of Henle and the upper part of the col- 

 lecting tubes form the little cones in the cortex, visible to the eye 

 and known as the pyramids of Ferrein. 



The Malpighian corpuscle consists of a spherical plexus or knot 

 of blood-vessels, the glomerulus, which is inclosed in the dilated end 

 of the urinary tubule, known as the capsule of Bowman. As the 

 capsule has been infolded by the glomerulus being pushed into it (as 

 one would infold the end of the finger of a glove by the tip of one's 

 finger), it follows that the capsule consists of two layers. The 

 internal one, covering the glomerulus closely, is formed of cubical 

 ce.Us, while the external one, formed of flat, polygonal cells, passes 

 on into the neck and thence forms the wall of the convoluted tubule. 

 The cells in this portion of the tube are shaped like a cone, the 

 narrow end being directed toward the lumen of the vessel; owing 

 to the fine, longitudinal lines upon each cell, it has a rodlike appear- 

 ance: rodded cell 



The Blood-vessels. The renal artery divides at the hilus into 

 four or five branches. The four or five main branches continue to 

 divide and subdivide and so pass into the parenchyma of the organ. 

 They course between the papilla? to run up to the boundary between 

 the medulla and cortex. Here the vessels bend at right angles to 

 form a series of loops or arches, their convexity toward the cortex 

 of the kidney. From the convex sides of the arches there spring 

 vessels at regular intervals termed interlobular, or radiate, arteries. 

 They sometimes run up so as to divide the cortex into small lobules, 

 coursing singly between each two medullary rays. These radiate 

 arteries give off numerous small branches which run at right angles, 

 each one entering a Malpighian corpuscle. It is usual for the point 

 of entrance of the artery to be diametrically opposite the point of 

 origin of the urinary tubule. These last-named vessels, the vasa 

 afferentia, break up into very fine vessels within the capsule to con- 

 stitute the glomerulus. They are supported by connective tissue, 

 and form a veritable tuft of capillary vessels. It is of interest to 

 note that each glomerulus is covered by a single layer of flat, 



