THE KIDNEY AND URINARY PASSAGES. 



167 



calary piece." Several of these intercalary pieces open into 

 a collective tube, and the latter combine into larger canals. 

 We have thus presented the whole connection of the kidney. 

 Heidenhain has quite 



recently made an interest- 

 ing discovery concerning 

 the epithelium of the con- 

 voluted uriniferous canals, 

 of the returning side of 

 the loop, and of the inter- 

 calary piece. Its proto- 

 plasm is in great part 

 metamorphosed into a con- 

 siderable number of very 

 fine cylinders or rods. 



Around the nucleus, 

 which these "rod cells" 

 invest, as well as between 

 the rods, there remains a 

 residue of unchanged pro- 

 toplasm. These rods, with 

 which the gland cells rest 

 on the membrana, give the 

 transverse section of these 

 uriniferous canals a radio- 

 striated appearance. 



The medullary rays pene- 

 trate the cortex, like groups 

 of pegs driven close to- 

 gether into a board. They 

 consist of two different 

 elements. In the first 



Fig. 154. — Diagram of the uriniferous canals in a 

 vertical section of the kidney; R, cortex: M, 

 medulla ; *. border : a, efferent canal-work, with the 

 system of branches b ; c. transition canal (or inter- 

 calary pieced in the ascending or returning side d\ 

 e. descending ; /, convoluted uriniferous canal of 

 the cortex ; g, capsule with the glomerulus. 



place we have the cortical branches of the efferent canal-work 

 of the medullary substance pushing forwards to near the sur- 

 face of the kidney ; these are accompanied by the upper 

 portions of the ascending looped canals, which have a smaller 

 diameter. 



