252 



HISTOLOGY. 



has the following history. It becomes subdivided into masses enveloping 

 the enlarged tips of the branching collecting tubules. Some of its cells 

 become arranged so as to form vesicles as shown in the section Fig. 282, 

 and in the reconstruction Fig. 283, A. In these the vesicle is independent 

 of the collecting tubule. In B and C it has become elongated making an 



S-shaped tubule, and has united with the col- 

 lecting tubule. A glomerulus develops in the 

 lower curve of the S and, as shown in the figures, 

 it gradually becomes enclosed in its capsule 

 the terminal part of the tubule. The glomer- 

 uli begin to form near the surface of the kidney 

 and become buried in the advancing cortex; the 

 oldest glomeruli are nearest the medulla. 



Between the capsule and the collecting 

 tubule, the tubule of mesenchymal origin be- 

 comes contorted or convoluted. One of the 

 loops in the midst of the coil elongates down- 

 ward toward the medulla, lying close beside 

 and parallel with the collecting tubules. This 

 Henle's loop (shown only in J of Fig. 283) is 

 lodged in the radiate part of the cortex and ex- 

 tends into the medulla. 



Three tubules of the adult, with capsules 

 situated in the outer, middle, and inner part of 

 the cortex respectively, are shown in the diagram 

 Fig. 284. Each capsule connects with a proxi- 

 mal convoluted tubule which is continuous with 

 the descending limb of Henle's loop, after hav- 

 ing extended toward the surface of the kidney 

 in the convolute part of the cortex. The de- 

 scending limb is essentially a straight tube of 

 small diameter, owing to the flatness of its cells 

 and not to a -narrowing of the lumen. The 

 portion of the proximal convoluted tubule 

 which descends in a straight course to join 



the descending limb is called the 'end segment' or 'spiral tubule.' The 

 descending limb generally becomes of large diameter before it turns to 

 become the ascending limb of Henle's loop. This returns to the immediate 

 neighborhood of its capsule, where it forms the distal convoluted tubule 

 [intercalated tubule]. By means of the 'junctional' or 'arched collecting 

 tubule' the distal convoluted joins the straight collecting tubule. The 



FIG. 284. DIAGRAM OF THREE 

 URINIPEROUS TUBULES AND 

 THEIR RELATION TO A COL- 

 LECTING TUBULE. (Huber.) 



a. 1., Ascending limb of Henle's 

 loop; c., capsule; c. t., collect- 

 ing tubule; d. c., distal convo- 

 luted tubule; d. 1., descending 

 limb; p. c., proximal convo- 

 luted tubule; p. d., papillary 

 duct. 



