THE URINARY TRACT. 



743 



NA 



chiefly the ascending branches, and of the collecting tubules, all 

 of which are fewer in number and of a less marked character the 

 nearer the surface of the kidney, the main bulk of which is occu- 

 pied by convoluted tubules. Sagittal sections of the pyramidal 

 substance are characterized by bundles of the vasa recta arranged 

 together with transverse sec- 

 tions of the narrow tubules, 

 both the ascending, descending, 

 and looped portion, around 

 which are grouped the trans- 

 verse sections of the collecting 

 tubules. The narrow tubules 

 become fewer, and the collect- 

 ing tubules wider the nearer 

 they approach the papilla. 

 (See Fig. 335.) 



Of the lymphatics of the kid- 

 ney very little is known. Some 

 authors claim that they are 

 clefts in the interstitial con- 

 nective tissue, while others de- 

 scribe rhomboidal meshes of 

 lymphatics, bounded by an en- 

 dothelial coat, around the urin- 

 iferous tubules. In the capsule 

 of the kidney there is a regular 

 lymphatic system, and in the hilus several large lymph- vessels 

 are found which are supplied with valves. 



The nerves of the kidney have been, for a number of months, 

 studied in my laboratory by Dr. M. Holbrook, who has not yet 

 completed his researches. He found a large number of nerves 

 accompanying the arteries and producing a reticulum around 

 the capillaries, in accordance with the statements of L. Beale. 

 Every tubule is accompanied by a reticulum of non-medullated 

 nerve-fibers, from which prolongations pass through the base- 

 ment-membrane, and produce a very narrow plexus close above 

 this membrane. From the intra-tubular plexus delicate branches 

 arise, running along the cement-substance of the epithelia, and 

 in union with the slender, transverse filaments traversing the 

 cement-substance and inter-connecting the epithelia. Such fibril- 

 lae are represented in Fig. 337. By Holbrook's specimens it is 

 plainly shown that every epithelium is in connection with a 



FIG. 334. CORTICAL SUBSTANCE OP 

 THE KIDNEY OF A DOG. SAGITTAL 

 SECTION. BLOOD-VESSELS INJECTED. 



C, convoluted tubule; N, narrow or loop- 

 tubule; NA, ascending branch of narrow tu- 

 bule ; 8, straight collecting tubule. Magnified 

 500 diameters. 



