212 THE MICROSCOPIST. 



the base of the pyramids these tubes curve upwards, 

 forming the looped tubes of Henle. The recurrent tubes 

 enlarge, and exhibit the ordinary cubical gland-cell. 

 These tubes also become more tortuous, and empty into 

 others of larger calibre, called collecting tubes. These 

 are lined with low columnar epithelium, and uniting with 

 similar tubes at acute angles, give exit to the urine at the 

 apex of the papillae in the pyramids (Plate XXIII, Fig. 

 170). 



The bloodvessels of the kidney are as complex as the 

 glandular tissue. Both vein and artery enter at the hilus 

 of the kidney, and after giving twigs to the external 

 tunic, proceed between the pyramids as far as their bases. 

 Here they give off curving branches, forming imperfect 

 arches among the arteries, and complete anastomosing 

 rings on the veins. From the arterial arcbes spring the 

 branches which bear the glomeruli of the cortical sub- 

 stance or Malpighian tufts (Plate XXIII, a, Fig. 171). 

 The afferent vessel of the glomerulus subdivides, and after 

 coiling and twisting w 7 ithin the capsule of Bowman, gives 

 origin to the efferent vessel, by the union of the small 

 branches thus formed. This efferent vessel breaks up into 

 a network of fine capillaries, with elongated meshes sur- 

 rounding the straight uriniferous canals. From the periph- 

 ery of this network somewhat wider tubes are given off, 

 which surround with rounded meshes the convoluted tubes 

 of the cortex. 



The long bundles of vessels between the uriniferous tubes 

 of the medulla, communicating in loops or forming a deli- 

 cate network round the mouths of the canals at the apex 

 of the papillse are called the vasa recta. 



The ureters, like the pelvis of the kidney, consist of an 

 external fibrous tunic, a middle layer of smooth muscular 

 fibres, and an internal mucous membrane with a layer of 

 epithelium. The bladder is covered externally with a 

 serous membrane, the peritoneum. The female urethra is 



