THE KIDNEYS AND VRINE. 



353 



This reflected layer of epithelium is readily seen in young subjects, but 

 cannot always be demonstrated in the adult. (See Figs. 244 and 245.) 



The vessels \viiich enter the medullary layer break up into smaller 

 arterioles, which pass through the boundary layer and proceed in a 

 straight course between the tubules of the papillary layer, giving off on 

 their way branches, which form a fine arterial meshwork around the tubes, 

 and end in a similar plexus, from which the venous radicles arise. 



Besides the small afferent arteries of the Malpighian bodies, there are, 

 of course, others which are distributed in the ordinary manner, for nutri- 

 tion's sake, to the different parts of the organ; and in the pyramids, be- 



FIG. 244. 



FIG. 245. 



lie and tuft, with the commencement of a 



FIG. 244. 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; 6, 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. 245. Epithelial elements or a Malpighian ca; 

 urinary tubule showing the afferent and efferent 

 capsule ; b, similar, but rather lar 

 the vessels of the capillary tuft 

 of it. (W. Pye.) 



tween the tubes, there are numerous straight vessels, the vasta recta, sup- 

 posed by some observers to be branches of vasa efferentia from Malpighian 

 bodies, and therefore comparable to the venous plexus around the tubules 

 in the cortical portion, while others think that they arise directly from 

 small branches of the renal arteries. 



Between the tubes, vessels, etc., which make up the substance of the 

 kidney, there exists, in small quantity, a fine matrix of areolar tissue. 



Nerves. The nerves of the kidney are derived from the renal plexus. 



Structure of the Ureters. The duct of the kidney, or ureter, is a 



tube about the size of a goose-quill, and from a foot to sixteen inches in 



length, which, continuous above with the pelvis of the kidney, ends 



below by perforating obliquely the walls of the bladder, and opening on 



VOL. I. 23. 



