256 HISTOLOGY'. 



From the preceding account it is evident that some parts of the urinary 

 tubules are easily recognizable and that others are not. The capsules, 

 descending limbs and the collecting tubules have distinctive characters. 



Large collecting ^^ . _^^ ^^^^ 



tubule. (T - Q 4f v 



^V^ Ti" 



^ 



* ) ~^*' * 



l -v. **> 



1 .C 





FIG. 288. FROM A TRANSVERSE SECTION" THROUGH THE MEDULLA OF A HUMAN KIDNEY. X 320. 



(Schaper.) 



In the medulla, since convoluted tubules are absent, the ascending limbs 

 (including the part of the descending limb which is of large diameter) 

 are likewise easily identified. In the cortex the proximal and distal con- 

 voluted tubules wind about one another and cannot be absolutely dis- 

 tinguished except by reconstructions. In Fig. 

 x^^^^%>v 2 &7' the tubules labelled ascending limb (?), 



/;.. %^\ found in the radiate part of the cortex, have 



/&- 'X also been labelled distal convoluted and end 



/. : : ../ A segment of the proximal convoluted; they can- 



not be distinguished from these in a single 



^^^ MJ^Bj section, but their position in the radiate por- 



^r.^/:i tion is in favor of regarding them as ascend- 



^HH ing limbs. 



The connective tissue about the kidney 



FIG. 289. CROSS SECTION OF A f , , . i i_ 



CONVOLUTED TUBULE FROM A forms a tatty capsule, cdpsuid ddiposd, which 



RABBIT. (Szymonowicz.) 



surrounds the renal pelvis, and its calyces ex- 

 cept where they receive the papillae. A dense fibrous capsule, tunicajibrosa, 

 is closely applied to the outside of the kidney, from which it may be stripped 

 off. It contains elastic fibers which increase in abundance with age, and 

 also smooth muscle fibers. Within the kidney each tubule is surrounded by 

 a small amount of connective tissue, in part reticular. It is more abundant 



