THE KIDNEYS AND SKIN. 431 



containing a tuft of small blood-vessels. Or, followed the 

 other way, each tubule commences in the cortex with a 

 globular dilatation, the Malpigliian capsule. From this it 

 continues as a convoluted tubule in the cortex; this passes 

 into a pyramid of Ferrein, becomes straight, and runs to near 

 a pyramid of Malpighi as the descending limb of a loop of 

 Henle. Turning at the loop, it continues as its ascending 

 limb, and this passes out again into the cortex and becomes 

 the convoluted junctional tubule, which passes as a straight 

 collecting tubule into a pyramid of Ferrein, where it joins 

 others to form an excretory tubule; the excretory tubules 

 run into the main pyramid and unite to form the discharging 

 tubules which open on the papilla. Throughout its course 

 the tubule is lined by a single layer of epithelium cells differ- 

 ing in character in its different sections: they are flat and 

 clear in the capsules, and very granular in both the convo- 

 luted parts, where their appearance suggests that they are 

 not mere lining cells but cells with active work to do; they 

 are non-granular and flat in the descending limb of the loop 

 of Henle, clear and columnar in most of the ascending, and 

 in both are probably only protective; in the collecting and 

 discharging tubules they are somewhat cuboidal in form and 

 have no active secretory function. All the tubes are bound 

 together by a sparse amount of connective tissue and by 

 blood-vessels to form the gland. The lymph spaces are large 

 and numerous, especially about the convoluted portions of the 

 tubules. 



The Blood-flow through the Kidney. The amount of 

 blood brought to the kidney is large relatively to the size of 

 the organ and enters under a very high pressure almost direct 

 from the aorta, and leaves under a very low, into the inferior 

 cava (Fig. 132). The final twigs of the renal artery in the 

 cortex, giving off a few branches which end in a capillary 

 network around the convoluted tubules and in the pyramids, 

 are continued as the afferent vessels of Malpighian capsules, 

 the walls of which are doubled in before them (Fig. 134); 

 there each breaks up into a little knot of capillary vessels 

 called the glomerulus, from which ultimately an efferent vessel 

 proceeds. Where the wall of the glomerulus, w, Fig. 134, is 

 doubled in before the blood-vessels, its lining cells continue 

 as a covering, c, to the latter, closely adhering to the vascular 

 walls. A space, A, is left between the epithelial cells of the 



