THE EXCRETION OF URINE 



509 



of the capsule varies with the activity of the kidney, as is shown in 

 the following figures given by Brodie and Mackenzie. 1 



The urinary tubule has a remarkable blood supply. The renal arteries 

 arise directly from the abdominal aorta and are very short. They run 

 through the medulla to the cortex, and join with neighboring arteries to 



B. 



Fig. 171. Cross sections of convoluted tubules from kidney of rat. A, during slight secretion; B, 

 during maximal secretion. (From Sauer.) 



form arches from which proceed branches, that radiate into the cortex 

 and give off smaller branches each of which very shortly breaks up into a 

 small capillary tuft, the glomerulus, which lies in the invaginated sphere 

 of Bowman's capsule. The capillaries collect into an efferent vessel, which 

 appears to be smaller than the afferent artery, and this vessel in emerging 

 from the capsule again breaks up to form a capillary network about the con- 

 voluted tubules, forming their sole blood supply. These capillaries 

 coalesce to form the renal vein. The blood of the kidney must, accord- 

 ingly, pass through two sets of capillaries. 



The kidney is richly supplied with nerves, which are for the most part 

 derived from the celiac ganglion and are in connection with the splanch- 



