PORTAL CIRCULATION OF THE KIDNEYS. 531 



Madder inferiorly, and with that of the tubuli 

 uriniferi above. 



Vessels and Nerves. The renal artery is derived 

 from the aorta ; it divides into several large branches 

 before entering the hilus, and within the organ ra- 

 mifies in an arborescent manner, terminating in 

 nutrient twigs, and in the small inferent vessels of 

 the corpora Malpighiana. In the Malpighian 

 bodies the inferent vessels divide into several pri- 

 mary twigs, which subdivide into capillaries, and 

 the capillaries, after forming loops, converge to the 

 efferent vein, which is generally smaller than the 

 corresponding artery. The efferent veins proceed 

 to and form a capillary venous plexus, which surrounds the tortuous tubuli 

 uriniferi, and from this venous plexus the blood is conveyed, by converg- 

 ing branches, into the renal vein. 



"Thus," remarks Mr. Bowman, "there are in the kidney two perfectly 

 distinct systems of capillary vessels, through both of which the blood 

 passes in its course from the arteries into the veins : the first, that" which 

 forms the vascular tuft in the Malpighian bodies, and is " in immediate 

 connexion with the arteries ; the second, that enveloping the convolutions 

 of the tubes and communicating directly with the veins. The efferent 

 vessels of the Malpighian bodies, that carry the blood between these two 

 systems, may collectively He termed the portal system of the kidney." 

 The inferences drawn by Mr. Bowman from his investigations are interest- 

 ing; they are, that the capillary tufts of the Malpighian bodies are the part 

 of the kidney specially acted on by diuretics ; that they are the medium 

 by which water, certain salts, arid other substances, pass out of the system ; 

 that they are, moreover, the means of escape of certain morbid products, 

 such as sugar, albumen, and the red particles of the blood. Respecting 

 the capillary venous plexus, we have proof that the principal proximate 

 constituents of urine, such as urea, lithic acid, &c., are, like the bile, de- 

 rived from venous (portal) blood. 



The Veins of the kidney commence at the surface by minute converging 

 venules, the stellated vessels, and proceed inwards, receiving in their 

 course the veins of the cortical and tubular portions of the organ. On 

 arriving at the pelvis, they unite to form the branches of the renal vein, 

 which terminates in the vena cava by a single large trunk on each side ; 

 the left renal vein receiving the left spermatic vein. Injections thrown 

 into the renal artery, and returning by the tubuli uriniferi, make their way 

 into those tubes by rupture. The lymphatic vessels terminate in the lum- 

 bar glands. 



The Nerves are derived from the renal plexus, which is formed partly 

 by the solar plexus, and partly by the lesser splanchnic nerve. The renaJ 

 plexus gives branches to the spermatic plexus, and branches which accom- 



* Plan of the renal circulation ; copied from Mr. Bowman's paper, a. A branch of 

 the renal artery giving off several Malpighian twigs. 1. An efferent twig to the capil- 

 lary tuft contained in the Malpighian body, m ; from the Malpighian body the urinife- 

 rous tube is seen taking its tortuous course to t. 2, 2. Efferent veins ; that which pro- 

 ceeds from the Malpighian body is seen to be smaller than the corresponding artery, 

 o, p. The capillary venous plexus, ramifying upon the uriniferous tube. This plexus 

 receives its blood from the efferent veins, 2, 2, and transmits it to the branch of the 

 renal vein, v. 



