212 



NORMAL HISTOLOGY. 



5. The connecting or junctional tubule effects the union of the uriniferous tubule 

 proper with the duct-system. It is narrower ( 23-25 fj.) than the preceding segment and 

 lined with well defined cuboidal cells, which being lower afford an increased lumen. 



After an usually short and somewhat 

 arched course, the connecting tubule 

 enters the medullary ray and, uniting 

 with similar canals, joins in forming 

 the collecting tubule. 



6. The collecting tubule at first 

 lies within the medullary ray, where 

 it represents the beginning of the 

 system of straight duct-tubes opening 

 on the papilla, and then passes into the 

 renal pyramid. During their course 

 through the medullary ray, the collect- 

 ing tubules repeatedly unite to produce 

 stems, which, while increasing four- or 

 five-fold in diameter, diminish in num- 

 ber as they descend in the medulla. 

 In consequence of this fusion, within the 

 pyramid the collecting tubules are dis- 

 posed in groups, each of which corre- 

 sponds to the tubules prolonged from a single medullary ray, surrounded by the 

 limbs of the loops of Henle. The groups are further separated by the bundles of straight 

 blood-vessels (vasa rectce) of the medulla. The epithelium lining the collecting 



Section across upper part of renal pyra- 

 'd-vessels surrounded by 



FIG. 264. 



mid, showing groups of hloo 

 uriniferous tubules. X 50. 



-N^S//^0 o e?\V>- If: -"-^' ' 'ftA h 



Blood-vessel 



Collecting 

 tubule 



FIG. 265. Section of medulla across renal pyramid, showing large collecting tubules, limbs of Rente's 

 loops, blood-vessels and intertubular stroma. X 130. 



tubules consists of clear, distinctly defined, cuboidal cells, whose height gradually 

 increases as the medulla is traversed. After converging to within about 5 mm. of the 

 apex of the papilla, the now large collecting tubules undergo repeated junction, 

 increasing in diameter (50-60 //) but rapidly diminishing in number, to form the wide 

 papillary ducts. 



