194 



THE ESSENTIALS OF HISTOLOGY. 



a vessel (junctional tubule, 12) which joins a straight or collecting tubule 

 (13). This now passes straight through the medullary substance of the 

 kidney (14) to open at the apex of the papilla as one of the ducts of 

 Bellini (15). 



FIG. 227. DIAGRAM OF THE COURSE OF TWO URINIFEROUS TUBULES. (Klein.) 



A, cortex ; B, boundary zone ; c, papillary zone of the medulla ; a, a', superficial and deep 

 layers of cortex, free from glomeruli. For the explanation of the numerals, see the text. 



The tubules are throughout bounded by a basement-membrane, which 

 is lined by epithelium, but the characters of the epithelium-cells vary 



