KIDNEY. 



[ 375 ] 



KIDNEY. 



and efferent vessels are usually situated near 

 each other, and opposite the origin of the 

 urinary tubule. 



The efferent vessels, which, although 

 arising from the capillaries of the Malpighian 

 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 

 surrounds closely the coiled tubules on all 

 sides, and forms a connected plexus through- 

 out the kidneys, 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. 



Mr. Bowman compares the solitary effe- 

 rent vessels of the Malpighian bodies to the 

 portal system of the liver, both serving to 

 convey blood between two capillary systems. 

 He describes these efferent vessels collect- 

 ively as the portal system of the kidney. 



The interstices between the vessels, nerves 

 and tubules of the kidney are occupied by a 

 stroma of areolar tissue (fig. 390 c), containing 

 elongated nuclei, and which is much more 

 abundant in the medullary than in the cortical 

 portion. At the surface this frequently be- 

 comes condensed to form a very distinct 



Fig. 390. 



Transverse section of some cortical urinary tubules ; 

 human . a, divided tubules, with the epithelium removed ; 

 b, the same, containing the epithelium; c, stroma of 

 areolar tissue ; d, space corresponding to a Malpighian 

 body. 



Magnified 350 diameters. 



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 areolar tissue, 

 mixed with elastic tissue. 



The muscular coat is strongest in the 

 ureter, and forms two layers of unstriated 

 fibres, the inner being transverse, the outer 

 longitudinal, but near the bladder an inner 

 layer of longitudinal fibres is added. The 

 muscular coat of the pelvis is as strongly 

 developed as that of the ureter, becoming, 

 however, less marked in the calyces, and 

 terminating where they embrace the pa- 

 pillae. 



The mucous coat is thin, and not furnished 

 with glands or papillae. Its epithelium (fig. 

 391, B) is laminated, and remarkable for the 

 variable form and size of its elements (fig. 

 391, A), the deeper cells being roundish and 

 small, those in the middle cylindrical or 

 conical, and the uppermost roundish, poly- 

 gonal, and somewhat flattened. The cells 

 frequently contain two nuclei, and bright 

 rounded granules with dark margins. 



Epithelium of the pelvis of the kidney ; human. 



A . Isolated cells : a, small, b, large pavement-epithelial 

 cells ; c, the same containing the granules ; d, cylindrical 

 and conical cells from the deeper layers ; e, intermediate 

 forms. B. Cells in situ. 



Magnified 350 diameters. 



