408 THE HUMAN BODY. 



0.125 mm. (-g-J-g- inch). Kunning into the pyramid from 

 this point each tubule divides several times. At first the- 

 branches are smaller than the main tube; but as soon as 

 they have come down to about 0.04 mm. (-^^ inch) this- 

 diminution in size ceases, and the division continuing 

 while the tubules retain the same diameter, the pyramid 

 thus gets, in part, its conical form. Ultimately each branch 

 runs somewhere out of the pyramid, either from its base or 

 side, into the cortex and there dilates and is twisted. It. 

 then narrows and doubles back again into the pyramid and 

 runs as a straight tube towards the papilla, but before reach- 

 ing it makes a loop, and turns back again as a straight tube 

 to the base of the pyramid, where it once more enters the- 

 cortex, dilates and becomes contorted, and then ends in 

 a spherical capsule, containing a tuft of small blood-vessels. 

 Or, followed the other way, each tubule commences in the- 

 cortex with a globular dilatation, the Malpighian capsule. 

 From this it continues as a convoluted tubule in the- 

 cortex; this passes into a pyramid, becomes straight, and 

 runs on as the descending limb of a loop of Henle. Turn- 

 ing at the loop, it continues as its ascending limb, and this 

 passes out again into the cortex and becomes the convoluted 

 functional tubule, which passes as a straight collecting 

 tubule into the pyramid and there joins others to form an 

 excretory tubule which opens on the papilla. Throughout 

 its course the tubule is lined by a single layer of epithelium 

 cells differing in character in its different sections. All the- 

 tubes are bound together by connective tissue and blood- 

 vessels to form the gland. 



The Blood-Flow through the Kidney. 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, are continued as the afferent vessels of Malpi- 

 ghian capsules, the walls of which are doubled in before them 

 (Fig. 116); there each breaks up into a little knot of 

 capillary vessels called the glomerulus, from which ulti- 

 mately an efferent vessel proceeds, and outside the capsule 

 this breaks up into a close capillary network among the con- 

 voluted tubes. From the capillaries the blood is collected 



