358 



HANDBOOK OF PHYSIOLOGY. 



intervals between the papillae, and at the junction between the cortex 

 and the boundary layer. The main branches then pass almost horizon- 

 tally, giving off branches upwards to the cortex and downwards to the 

 medulla. The former are for the most part straight ; they pass almost 

 vertically to the surface of the kidney, giving off laterally in all direc- 

 tions longer or shorter branches, which ultimately supply the Malpi- 

 ghian bodies. 



The small afferent artery (Figs. 247 and 249) which enters the Malpi- 

 ghian corpuscle, breaks up in the interior as before mentioned into a 

 dense and convoluted and looped capillary plexus, which is ultimately 

 gathered up again into a single small efferent vessel, comparable to a 

 minute vein, which leaves the capsule just by the point at which the 

 afferent artery enters it. On leaving, it does not immediately join other 



FIG. 248. 



FIG. 249. 



Fia. 248. Transverse section of a developing Malpighian capsule and tuft (human) x 300. From 

 a foetus at about the fourth month ; a, flattened cells growing to form the capsule ; &, more rounded 

 cells; continuous with the above, reflected round c, and finally enveloping it; c, mass of embryonic 

 cells which will later become developed into blood-vessels. (W. Pye.) 



FIG. 249. Epithelial elements of a Malpighian capsule with tuft, with the commencement of a 

 urinary tubule showing the afferent and efferent vessel ; a, layer of tesselated epithelium forming 

 the capsule; 6, similar, but rather larger epithelial cells, placed in the walls of the tube; c, cells cov- 

 ering the vessels of the capillary tuft; d, commencement of the tubule, somewhat narrower than 

 the rest of it (W.Pye.) 



small veins as might have been expected, but again breaking up into a net- 

 work of capillary vessels, is distributed on the exterior of the tubule, 

 from whose dilated end it had just emerged. After this second break- 

 ing up it is finally collected into a small vein, which, by union with 

 others like it, helps to form the radicles of the renal vein. 



Thus, in the kidney, the blood entering by the renal artery, traverses 

 two sets of capillaries before emerging by the renal vein, an arrangement 

 which may be compared to the portal system in miniature. 



The tuft of vessels in the course of development is, as it were, thrust 



