126 PRACTICAL MICROSCOPY. 



orterioles which emerge from the capsule close to the afferent vessel. 

 The latter is the more noticeable, as it is usually much the largest. 

 The efferent arteriole immediately breaks up into a second capillary 

 plexus, which courses between the uriniferous tubules of the 

 labyrinths and of the pyramids of Ferrein. This second plexus also 

 descends between the elements of the pyramids of Malpighii. From 

 the arteries forming the arcade another set of branches the arterialce 

 rectce is given off; which, descending into the Malpighian pyramids, 

 provides another and direct arterial supply to the tubular elements 

 by elongate capillary loops. 



The course of the venous trunks is not unlike that pursued by the 

 arteries. Interlobular veins pass into a venous arcade ; the former 

 lying in the cortical labyrinths parallel with and close to the arteries. 

 In the medulla the venous blood is collected from the capillaries and 

 carried to the bases of the Malpighian pyramids in small veins venulae 

 rectae. The blood from the cortical intertubular capillaries is col- 

 lected in the interlobular veins. 



A peculiar vascular arrangement exists just beneath the capsule of 

 the kidney, consisting of scattered venous plexuses, the stars of 

 Verheyen. They contain blood collected from contiguous inter- 

 tubular capillaries and are in connection with the summits of the 

 interlobular veins. 



From what has been said, it will be seen that the cortical and 

 medullary blood- supplies are, to a certain extent, independent of one 

 another. The arteriolae rectae provide a vascular supply to the 

 elements of the Malpighian pyramids even after many of the glomer- 

 uli have become obliterated by disease. 



Nerve and lymphatic elements are not very prominent features in 

 sections of the kidney. Small medullated nerve trunks may be easily 

 demonstrated in transverse sections of the cortex, especially near the 

 bases of the medullary pyramids, where they will be seen, in company 

 with the blood-vessels of the arcades. Lymph channels are also to be 

 seen in the vicinity of the vessels of the hilum, and in the connective 

 tissue of the capsule. The nervous system of the kidney would prove 

 a valuable field of labor, and would well repay the advanced student's 

 patient and earnest investigation. 



' The histology of the kidney will be better comprehended by a 

 reference to its functioning. The separation from the blood of a 

 quantity of water, together with certain excrementitious matters, is 

 effected, partly in the Malpighian bodies, and partly in the tubules. 

 The vascular tuft the glomerulus is covered with a close fitting 

 membrane composed of flat cells. The blood in this plexus parts 



