THE URINARY ORGANS. 265 



not only other junctional tubules but also unites 

 with other collecting tubes. The junctional part is 

 narrow but its lumen relatively large, being lined by 

 clear flat or cubical cells. The collecting tubes are 

 large and have a lining of simple cubical epithelium. 

 The location of the different parts of the kidney 

 tubules may be tabulated as follows : 



Portion of Tubule. Location. 



1. Bowman's capsule. cortical labyrinth. 



2. Neck cortical labyrinth. 



3. Proximal convoluted cortical labyrinth. 



4. Spiral portion medullary rays. 



5. Loop of Henle : 



(a) Descending limb medulla. 



(b) Loop medulla. 



(c) Ascending limb medulla and medullary rays. 



6. Irregular part cortical labyrinth. 



7. Distal convoluted cortical labyrinth. 



8. Junctional tubule medullary rays. 



9. Collecting tubule medullary rays and medulla. 



It will be observed that the walls of these tubules 

 consist of simple epithelium ; that this is made up of 

 pavement cells in the capsule, neck, and descending 

 limb of Henle 's loop ; while large cubical or columnar 

 cells with granular and rod-like structure of the cyto- 

 plasm are found in the convoluted parts and ascend- 

 ing limb of Henle 's loop; and a low cubical epithe- 

 ^ium invests the junctional and collecting tubules. 



Casts. It is common in high fevers and in diseases 

 of the kidney to find moulds of the uriniferous 

 tubules in the urine. In high fevers blood may 

 enter and congeal in the uriniferous tubules, the 

 kidney secretion forces out .this obstruction, which 

 then appears in the urine as a blood cast. A clear 

 serum mould is called a hyaline cast. In more 

 chronic cases the cells of the tubules are carried away 



