534 



THE URINARY APPARATUS. 



[CH. xxxvi. 



In the neck the epithelium is still flattened, but in some animals, 

 like frogs, where the neck is longer, the epithelium is ciliated. 



In the first convohited 

 and spiral tubules, it is 

 thick and the cells show 

 a fibrillated structure, ex- 

 cept around the nucleus, 

 where the protoplasm is 

 granular. The cells inter- 

 lock laterally and are diffi- 

 cult to isolate. In some 

 animals they are described 

 as ciliated. In the narrow 

 descending tubule of Henle 

 and in the loop itself, the 

 cells are clear and flattened 

 and leave a considerable 

 lumen ; in the ascending 

 limb they again become 

 striated and nearly fill the 

 tubule. In the zigzag and 

 second convoluted tubules 

 the fibrillations become 

 even more marked. The 

 junctional tubule has a 

 large lumen, and is lined 

 by clear flattened cells ; 

 the collecting tubules and 

 ducts of Bellini are lined 

 by clear cubical or col- 

 umnar cells. 



Blood - vessels of 

 Kidney. The renal 

 artery enters the kidney 

 at the hilus, and divides 

 into branches that pass 

 towards the cortex, then 

 turn over and form incom- 

 plete arches in the region 

 between cortex and me- 

 dulla. From these arches 



vessels pass to the surface which are called the interlobular arteries ; 

 they give off vessels at right angles, which are the afferent 

 vessels of the glomeruli ; a glomerulus is made up of capillaries as 



Fig. 422. Vascular supply of kidney, a, part of 

 arterial arch ; ft, interlobular artery ; c, glomeru- 

 lus ; d, efferent vessel passing to the medulla as 

 false arteria recta ; , capillaries of cortex ; /, 

 capillaries of medulla ; g, venous arch ; h, straight 

 veins of medulla ; i, interlobular vein ; j, vena 

 stellula. (Cadiat.) 



