KIDNEY. 



[ 449 ] 



KIDNEY. 



The efferent vessels, which, although 

 arising from the capillaries of the Malpi- 

 ghian tufts, are rather small arteries than 

 veins, in import and partly in structure, 

 terminate in the capillary network situated 

 in the cortical substance and the pyramids. 

 This network closely surrounds the coiled 

 tubules on all sides, and forms a connected 

 plexus throughout the kidney, the meshes 

 of which are roundish-angular ; but near 

 the pyramids the afferent vessels are larger, 

 and differ from the rest in their straighter 

 course and more sparing ramification. 



The veins of the kidney commence on 

 the surface of the organ and at the apices 

 of the papillae by small branches connected 

 with the plexus ; these by their union form 

 larger ones, which accompany the larger 

 arteries. 



Bowman compares the solitary efferent 

 vessels of the Malpighian bodies to the portal 

 system of the liver, both serving to convey 

 blood between twc capillary systems ; and 

 so these efferent vessels collectively form 

 the portal system of the kidney. 



The interstices between the vessels, nerves, 

 and tubules of the kidney are occupied by a 

 stroma of connective tissue (fig. 386 c), con- 

 Fig. 386, 



Transverse section of the cortical urinary tubules; 

 human, a, divided tubules, with the epithelium re- 

 moved ; 6, the same, containing the epithelium ; c, 

 stroma of connective tissue ; d, space corresponding to 

 a ilalpighian body. 



Magnified 250 diameters. 



taining elongated nuclei, and which is much 

 more abundant in the medullary than in the 

 cortical portion. At the surface this fre- 

 quently becomes condensed to form a very 

 distinct membrane, but loosely adherent to 



the fibrous capsule, and which is connected 

 by numerous delicate processes with the 

 inner stroma. 



The pelvis of the kidney with the calyces 

 and the ureter consist of an outer fibrous, a 

 muscular, and a mucous coat. The fibrous 

 coat is composed of ordinary connective 

 tissue, mixed with elastic tissue. 



The mucous coat is thin, and not fur- 

 nished with glands or papillae. Its epithe- 

 lium (fig. 387 B) is laminated, and remark- 



Epithelium of the pelvis of the kidney ; human. 



A. Isolated cells: a, small, 6, large pavement-epithe- 

 lial cells ; c, the same containing the granules ; d, cy- 

 lindrical and conical cells from the deeper-layers ; e, 

 intermediate forms. B. Cells in sUu. 



Magnified 350 diameters. 



able for the variable form and size of its 

 elements (fig. 387 A), the deeper cells being 

 roundish and small, those in the middle 

 cylindrical or conical, and the uppermost 

 roundish, polygonal, and somewhat flat- 

 tened. The cells frequently contain two 

 nuclei, and bright rounded granules with 

 dark margins. 



Lymphatics accompany the blood-vessels 

 at the hilum, and pass between the groups 

 of tortuous tubules in the cortex ; and the 

 nerves penetrate the kidney with the ves- 

 sels, and present ganglia in their course. 



In the Mammalia generally the structure 

 of the kidneys agrees essentially with that 

 of man. 



In the lower Vertebrata they exhibit 



