i882 



HUMAN ANATOMY. 



on gaining the Malpighian corpuscle the ascending limb crosses the neck in close proximity to 

 the glomerulus, with which it is connected by twigs from the vas eflferens (Hamburger i), and 

 then arches over the corpuscle to end in the succeeding convoluted tubule. The position of 

 the sudden transition from the narrow into the wider tube of Henle's loop varies, the change 

 exceptionally occurring after the turn is reached, sometimes within the loop itself, but most fre- 

 quently within the descending limb a short distance above the loop. 



5. The Distal Convoluted Tubule. — On gaining the level of the corresponding Malpighian 

 body, the ascending limb gradually widens into the distal convoluted or intermediate tubule, a 

 canal approximating the diameter (.040-. 045 mm.) of the surrounding convoluted tubules, but 

 differing from the latter in its wider lumen and in the character of its epithelium. This consists 

 of well-defined cuboidal cells, with spherical nuclei, the cytoplasm of which, while granular, is 



comparatively clear and devoid of stria- 



FiG. 1607. 



tions. The moderately tortuous path of 

 the intermediate tubule is marked by a 

 number of abrupt changes in direction, 

 but in general lies for a time enclosed by 

 the arch described by the corresponding 

 convoluted segment (Schweiger-Seidel), 

 which it finally crosses (Huber). 



6. The Connecting Tubule. — This 

 portion of the tubule (.023-. 025 mm. in 

 diameter) resembles the preceding seg- 

 ment in its clear epithelium, the lining 

 cells, however, being lower, with a cor- 

 responding increased lumen. After a 

 short and usually arched course, the con- 

 necting tubule enters the medullary ray 

 and, uniting with similar canals, joins in 

 forming the collecting tubule. 



7. The Collecting Tubule.— This 

 first lies within the medullary ray, where 

 it forms the beginning of the system of 

 straight duct-tubes that culminates in 

 the canals opening upon the papilla, 

 and then passes into the renal pyramid. 

 During their course through the medul- 

 lary ray the collecting tubules repeatedly 

 unite to produce stems, which, while in- 

 creasing four- or fivefold in diameter, are 

 diminishing in number. In consequence 

 of this fusion within th.e pyramid, the col- 

 lecting tubules are disposed in groups 

 (Fig. 1609), each of which corresponds 

 to the tubules prolonged from a single 

 medullary ray and is surrounded by the 

 limbs of the loops of Henle. On enter- 

 ing the renal pyramid, the groups of col- 

 lecting tubules at first are separated by 

 the intervening bundles of straight blood- 

 vessels {z'asa rectcr) that are given off 

 from the larger twigs within the boun- 

 dary zone for the supply of the medulla. 



After passing to within about 5 mm. of the apex of the papilla, towards which they converge, 

 the large collecting canals undergo repeated junction, increasing in diameter but rapidly dimin- 

 ishing in number, to form the wide papillary ducts. The epithelium lining the collecting tubules 

 — the larger as well as the smaller — consists of clear cuboidal or low columnar cells, sharply 

 defined from one another and provided with spherical nuclei. The light-colored cytoplasm 

 and distinct demarcation of these elements render the collecting tubules conspicuous and their 

 recognition easy. 



8. The Papillary Ducts. — These, the final segments of the kidney tubules, number from 

 ten to eighteen for each single papilla, at the apex of which they end. Each is formed by the 

 junction of from ten to thirty of the larger collecting tubules (.050-.060 mm.) and attains a 

 diameter of from .2-.3 mm. The lining epithelium is composed of conspicuous, clear columnar 

 cells, about .020 mm. in height and one-third as much in width, which rest upon a distinct 



Collecting 

 tubule 



Henle's 

 loop 



Longitudinal section of renal medulla, showing Henle's 

 loops and collecting tubules. X 45. 



1 Archiv f. Anat. u. Entwick., Suppl. Bd., 1890. 



