EXCRETION". 



463 



'& (figs. 289, 294), composed of a hyaline membrana propria, thickened 

 by a varying amount of fibrous tissue, and lined by flattened nucleated 

 epithelial plates. This capsule is the dilated extremity of the urinif- 

 erous tubule, and contains within it a glomerulus of convoluted capil- 

 lary blood-vessels supported by connective tissues, and covered by flat- 

 tened epithelial plates. The glomerulus is connected with an efferent 

 and an afferent vessel. (2) The constricted neck of the capsule (fig. 

 289, 2), lined in a similar manner, connects it with (3) The Proximal 

 convoluted tubule, which forms several distinct curves and is lined with 



71 









Smith.) 



short columnar cells, which vary somewhat in size. The tube next 

 passes almost vertically downward, forming (4) The Spiral Tubule, 

 which is of much the same diameter, and is lined in the same way as 

 the convoluted portion. So far the tube has been contained in the cortex 

 of the kidney; it now passes vertically downward through the most 

 external part (boundary layer) of the Malpighian pyramid into the more 

 internal part (papillary layer), where it curves up sharply, forming 

 altogether the (5 and 6) Loop of Henle, which is a very narrow tube 

 lined with flattened nucleated cells. Passing vertically upward just as 

 the tube reaches the boundary layer (7), it suddenly enlarges and be- 

 comes lined with polyhedral cells. (8) About midway in the boundary 



