MECHANISM OF THE PRODUCTION OF URINE. 



401 



vessels of the Malpighian tuft and the capillary plexus surrounding the tubes, the portal 

 system of the kidney. These intermediate vessels form a coarse plexus surrounding the 

 prolongations of the pyramids of Ferrein into 

 the cortical substance. 



The renal, or emulgent vein takes its origin 

 in part from the capillary plexus surrounding the 

 convoluted tubes and in part from the vessels 

 distributed in the pyramidal substance. A few 

 branches come from vessels in the envelopes of 

 .the kidney, but these are comparatively unim- 

 portant. The plexus surrounding the convoluted 

 tubes empties into venous radicles, which pass 

 to the surface of the kidney, and these present a 

 number of little radiating groups, each converg- 

 ing toward a central vessel. This arrangement 

 gives to the vessels of the fibrous envelope of the 

 kidney a peculiar stellate appearance. These are 

 sometimes called the stars of Verheyn. The 

 large trunks which form the centres of these 

 stars then pass through the cortical substance to 

 the rounded bases of the pyramids, where they 

 form a vaulted, venous plexus corresponding to 

 the arterial plexus already described. The ves- 

 sels distributed upon the straight tubes of the 

 pyramidal substance form a loose plexus around 

 these tubes, except at the papillae, where the net- 

 work is much closer. They then pass into the 

 plexus at the bases of the pyramids to join with 

 the veins from the cortical substance. From this 

 plexus, a number of larger trunks arise and pass 

 toward the hilum in the centre of the inter-py- 

 ramidal substance, enveloped in the same sheath 

 with the arteries. Passing thus to the pelvis of 

 the kidney, the veins converge into from three 

 to four great branches, which unite to form the 

 renal, or emulgent vein. A preparation of all 

 the vessels of the kidneys shows that the veins 

 are much more voluminous than the arteries. 



The lymphatics of the kidney are few, and, 

 according to Sappey, they only exist in the sub- 

 stance of the organ, converging toward the hilum. 

 This author does not admit the existence of su- 

 perficial lymphatics. 



The nerves are quite abundant and are de- 

 rived from the solar plexus, their filaments following the artery in its distribution in the 

 interior of the organ and ramifying upon the walls of the vessels. 



FIG. 116. Blood-vessels of the Malpighian bodies 

 and convoluted tubes of the kidney. (Sappey.) 



1, 1, Malpighian bodies surrounded by the capsules 

 of M filler; 2, 2, 2, convoluted tubes connected 

 with the Malpighian body ; 3, artery branch- 

 ing to go to the Malpighian bodies ; 4, 4, 4, 

 branches of the artery ; 6, 6, Malpighian bodies 

 from which a portion of the capsules has been 

 removed; 7. 7, 7, vessels passing out of the 

 Malpighian bodies ; 8, vessel, the branches ol 

 which (9) pass to the capillary plexus (10). 



Mechanism of the Production and Discharge of Urine. 



The striking peculiarities which the kidney presents in its structure, as compared with 



the true glands, and the fact of the voluntary discharge of its secretion at certain intervals, 



would naturally lead to a closer study of the mechanism of the production and discharge 



of the urine than we have given under the general head of the mechanism of the formation 



26 



