522 



MANUAL OF HISTOLOGY. 



propria of the capsule is excessively thin over the glomerulus, and 

 more like a homogeneous connective-substance or delicate boundary layer 

 of the whole. 



Turning our attention now particularly to the epithelial lining, we at 

 once recognise the fact that the thick granular gland cells of the convo- 

 luted tubes become transformed, at 

 the entrance to the capsule, into deli- 

 cate pavement epithelial elements (fig. 

 515, e), which line the whole internal 

 surface of the capsule, and may be- 

 easily rendered visible by the aid of a 

 solution of nitrate of silver (fig. 516, 

 g}. Among the lower vertebrates a 

 number of ciliated cells are arranged 

 around the entrance of the capsule, a 

 most 'fragile species of ciliated epi- 

 thelium (fig. 515, d). 



But the cellular layer said to exist 

 over the glomerulus, is far more dif- 

 ficult of recognition, and has not as 

 yet been satisfactorily demonstrated. 

 Nuclei are easily seen in this situation, 

 but the borders of cells are not to be 

 made out in the adult. From the fact 

 that distinct cells are seen upon the 

 glomerulus in the foetus, it has been 

 supposed that they may have become 

 fused together into one homogeneous 

 nucleated membrane (Scliweigger- 

 SeideT). Other observers, on the other 

 hand, have described here a complete covering of distinctly separate cells, 

 and have even put forward statements in regard to their size as com- 

 pared to the epithelial cells of the capsule. Our own experience inclines 

 us to the belief that they are correct in their views (fig. 516,/). 



272. 



From the preceding section we have learned that the convoluted tube 

 is an important element of the cortex, and takes its origin from the 

 capsule of the glomerulus. Leaving the destination of its other end for 

 the present undecided, let us turn our attention in the meantime to those 

 other constituents of the cortical portion of the organ whose position 

 and coarser structure have been already touched on ( 270) ; we allude to 

 the pyramid processes or medullary radii. 



We may easily satisfy ourselves that, in these bundles of straight 

 canals we have before us some of the open tubes of the medullary 

 pyramids, which, after passing through the so-called boundary layer, 

 arrive either singly, or, more rarely, in twos, in each of the processes, and 

 traverse the latter from below upwards, nearly to the surface of the 

 kidney. These passages, remarkable for their considerable calibre (fig. 

 517, a), have received the appropriate name of collecting tul)es (Ludwig). 

 They are lined by transparent low columnar epithelium, which we have 

 already seen in the last branches of the open medullary canals ; this is, 

 however, less characteristic here than in the situation just alluded to. 



Fig. 516. A glomerulus from the rabbit, a, 

 vasafferens; 6, vasefferens; c, glomerulus; 

 d, undermost portion of capsule without epi- 

 thelium ; e, neck ; /, epithelium of the glo- 

 merulus ; and g, that of the internal surface 

 of the capsule alter treatment with nitrate of 

 silver. 



