THE RENAL DUCTS. 215 



(3) through the deep cortical veins that traverse the inner third of the cortex 

 and are direct tributaries of the venae arciformes. The medulla is drained by 

 the venulae rectae, straight vessels that begin in the medullary capillary net- 

 work and empty, for the most part indirectly, in the arcuate veins. The 

 latter terminate in the larger interlobar veins, which accompany the corre- 

 sponding arteries along the sides of the pyramids and emerge into the sinus 

 around the papillae to become tributary to the renal vein. This vessel and 

 its branches are without valves. 



The lymphatics of the kidney occur as deeper and superficial networks. 

 The deep lymphatics arise as networks of capillaries within the cortex and 

 medulla, the general path of the more definite lymph-channels being that of 

 the blood-vessels, from four to seven large trunks emerging at the hilum. 

 The superficial lymphatics include two networks, one situated within or 

 beneath the fibrous capsule and the other within the perirenal fatty areolar 

 tissue (capsula adiposa). The subcapsular channels communicate with the 

 peripheral parts of the cortical network, as well as with the vessels outside 

 the fibrous capsule. 



The nerves supplying the kidney are derived from the renal sympathetic 

 plexus and consist, therefore, principally of nonmedullated fibres. These 

 accompany the blood-vessels, around which they form plexuses containing 

 ganglion-cells, and to which they send filaments for the walls. The smaller 

 arteries are accompanied by the nerves as far as the glomeruli and capillaries. 

 The relation between the nerve-fibres and the tubules is intimate, delicate 

 filaments enclosing the convoluted canals with a network outside the base- 

 ment membrane (epilemmar plexus), from which filaments pass to the inner 

 side of the membrane (hypolemmar) and end partly between the epithelial 

 cells. 



THE RENAL DUCTS. 



Each canal consists of the greatly expanded upper end, the renal pel-vis 

 with its subdivisions, the calyces, and the main part of the duct, the ureter, 

 the whole serving for the collection of the urine as it escapes from the kidney 

 and its transmission to the bladder. 



The wall of all parts of the renal duct is the same in its general structure 

 and consists of three layers: (i) the -mucous membrane, (2) the muscular 

 tunic, and (3) the fibrous coat; the mucous and muscular layers are more or 

 less blended, so that a distinct submucosa is wanting. The mucous mem- 

 brane is clothed with transitional epithelium consisting of several strata of 

 cells, the deepest elements being irregularly columnar and the superficial 

 ones to a varying degree flattened. The tunica propria is made up of 

 bundles of fibrous tissue, intermingled with comparatively few elastic fibres, 

 and is often directly attached to the muscular coat, a meagre amount of 

 loose fibre-elastic tissue in places suggesting a submucous layer. Within 

 the ureter, the mucous membrane is usually thrown into longitudinal folds 

 and, hence, the lumen appears stellate in transverse sections. Neither well 

 marked papillae nor true glands are present, although in places the tunica 

 propria encroaches upon the epithelium and subdivides the latter into nest- 

 like groups of cells. Numerous scattered colorless blood-cells are ordinarily 

 encountered within the tunica propria; sometimes, particularly in the vicinity 

 of the calyces, they are aggregated into distinct minute lymph-nodules. 

 On the papillae, the epithelium lining the calyces is continuous with that of 

 the papillary canals, while the tunica propria blends with the intertubular 

 renal stroma. 



