URETERS. 343 



capsules of Bowman. The straight tubes in the medullary sub- 

 stance are the tubes of Bellini; the convoluted ones in the 

 cortical substance, the tubes of Ferrein ; while the looped ones 

 are the tubes of Henle. At the base of the pyramids the straight 

 tubes form small bundles or fasciculi, which are prolonged into 

 the cortical substance as the pyramids of Ferrein. The tubuli 

 uriniferi consist of a membranous wall of varying thickness, lined 

 by epithelium, which in the straight tubes is columnar in form. 



Blood is supplied by the renal artery, nerves by the solar 

 plexus; the latter ramify round the arteries. The superficial 

 lymphatics are situated on the external surface, and pass into the 

 lumbar glands ; the deep-seated ones accompany the blood-vessels. 



The function of the kidneys is to secrete the urine, a fluid 

 consisting of water, holding in solution a varying quantity of 

 earthy salts, and a peculiar nitrogenous substance. Urea, which, if 

 not eliminated, acts as a blood-poison. Strange to say, this effete 

 material is secreted from arterial, or comparatively pure blood. 



SUPRARENAL CAPSULES. 



These are two small, flat, reddish-brown glandular botlies, about 

 two inches long, attached to the anterior borders of the kidneys. 

 They are ductless, larger in the foetus than in the adult, and 

 consist of a fibrous membrane covering a parenchyma, which 

 consists of an external cortical and an internal medullary sub- 

 stance. The external substance is brown in colour ; the medullary 

 is yellowish, soft, pulpy, nucleated and granular. The function 

 of these glands is unknown. They are larger in the foetus than 

 in the adult, and are said to be replaced if removed. 



URETERS. 



The ureters, the excretory ducts of the kidneys, are two 

 membranous canals, which convey the urine from the pelvis of 

 the kidney to the bladder. They consist of three coats ; an 

 external fibro-cellular, a middle muscular, and an internal mucous, 

 lined with epithelium similar to that of the bladder. On leaving 

 the hilus, they are directed towards the pelvic cavity, alongside 

 the aorta on one, and the posterior vena cava on the other side, 

 and between the peritoneum and the abdominal roof. On arriving 

 at the termination of the aorta, they cross the iliac arteries, covered 



