150 EXCRETION. 



The researches of late anatomists, however, particularly in 

 Germany, have shown that this simple view of the course 

 and termination of the tubes of the cortical substance must 

 be somewhat modified ; though as far as the anatomy of the 

 organ has any bearing upon our ideas concerning the mech- 

 anism of the secretion of urine, the views of physiologists 

 need undergo no material change. However interesting the 

 subject might be, it would be out of place to follow out 

 critically and in detail all the recent investigations into the 

 anatomy of these parts, and we will simply describe the 

 structure, direction, and relations of the tubes of the cortical 

 substance, as they appear from the most reliable modern in- 

 vestigations. 



The tubes of the cortical substance present considerable 

 variations in size, and instead of a single system continuous 

 with the straight tubes and terminating in the Malpighian 

 bodies, we can distinguish three well-defined varieties : 



1. The ordinary convoluted tubes, directly connected 

 with the Malpighian bodies. 2. Small tubes, continuous 

 with the convoluted tubes, dipping down into the pyramids 

 and returning to the cortical portion in the form of loops. 3. 

 Large, communicating tubes, forming a plexus connecting 

 the different varieties of tubes with each other and finally 

 with the straight tubes of the pyramidal portion. 



The relation of these tubes can be better understood by 

 reference to Fig. 7, taken from a recent work by Dr. Ch. F. 

 Gross. 1 This represents diagrammatically the course of a 

 uriniferous canal in the human subject. 1, Surface of a renal 

 papilla ; 2, Surface of the kidney ; 3, Boundary of the pyra- 

 midal substance; a, a, Malpighian corpuscles; &, Z>, Convo- 

 luted tubes ; <?, <?, Straight portion of the tubes ; d, d, Narrow 

 tubes of Henle ; , 0, Loops ; /, /, Large tubes of Henle ; 

 <7, <?, Communicating tubes, uniting with several others to 

 form A, a tube of Bellini. 



In tracing out the course and the relations of the tubes, 



1 GROSS, Essai sur la structure microscopique du rein, Strasbourg, 1868. 



