

COURSE AND DIAMETER OF THE URINARY TUBULES. 85 



URINARY TUBULES. 



1. COURSE AND DIAMETER. In consequence of their frequent 

 change of direction, the tubuli uriniferi pursue a relatively 

 long course in the substance of the kidney; and in one part 

 they may be seen to be isolated, whilst in another they coalesce 

 with others to form common trunks. -At certain points their 

 diameter varies to a considerable extent. 



Every tubulus uriniferus commences in the labyrinth by 

 means of a spheroidal enlargement, which constitutes the cap- 

 sule of a renal corpuscle or glomerulus. This is continuous 

 by a constricted portion the neck of the capsule with a 

 wide tube that runs with manifold windings towards the me- 

 dulla ; on reaching the margin of the medullary portion the 

 tortuous and wide tubule suddenly becomes attenuated, and 

 runs as a fine and straight canal to a variable distance into the 

 medulla (forming the descending or closed limb of the loop), 

 where it forms a narrow loop termed Henle's loop, returning 

 again towards the cortex by a similar straight canal (the 

 ascending or open limb of the loop). The recurrent limb of 

 the loop does not return exactly to the point from which the 

 opposite limb commenced, but as it were avoids the labyrinth, 

 and applies itself closely to the nearest medullary ray. 

 Sooner or later, however, it leaves this straight course, and 

 makes numerous angular windings, constituting the so-called 

 intermediary portion between the sinuous canals of the laby- 

 rinth. From thence it returns, after forming an arch, the 

 convexity of which is directed towards the surface of the 

 kidney, to the medullary ray, where its independent course 

 terminates. The mode in which this occurs is that several 

 canals running from various quarters to the same point coalesce 

 to form one of the straight and wide collecting tubules. 



Before we follow this last any further, the numerous varia- 

 tions in diameter that the tubules experience from their first 

 emergence from the cortex to their final return to the medul- 

 lary ray or to their junction with the collecting tubes must be 

 noticed. It has already been stated that the canal, where it 

 ceases to be tortuous, and extends towards the loop of Henle, 

 undergoes considerable attenuation. The distance that it 



