EXCRETION 



399 



(with its continuation, the spiral tubule), and ends in the cortex with 

 the distal convoluted tubule, the connection between the two being 

 made by a long loop (Henle's) with a descending and an ascending 

 limb (Fig. 125). 



The distal convoluted tube joins by means of the short con- 

 necting tubule one of the straight tubules which form the pyramids 

 of Ferrein or medullary rays in the cortex, and which run down 

 into the medulla, always uniting into larger and larger tubes as. 



FIG. 126. FROM A VERTICAL SECTION OF DOG'S KIDNEY TO SHOW THE 

 STRUCTURE OF DIFFERENT PORTIONS OF THE RENAL TUBULE (KLEIN). 



a, Bowman's capsule enclosing glomerulus, th<> cap'llaries of which are arranged in 

 lobules separated by a little connective tissue. The capsule and glomerulus together 

 constitute a Malpighian body or corpuscle ; n, neck of capsule ; c, c, convoluted tubules, 

 cut in various directions ; b, irregular or zigzag tubule ; d, e, and/ are straight tubules, 

 which take part in the formation of a medullary ray or pyramid of Ferrein ; d, collect- 

 ing tubule . e, e, spiral tubule ;/, narrow part of ascending limb of Henle's loop-tubule ; 

 c and e are lined with rodded epithelium. 



they go, until at length they open as ducts of Bellini on the 

 apex of a papilla. The two convoluted tubules and the 'ascend 

 ing limb of Henle's loop are lined by similar epithelial cells with 

 granular contents and a striated or 'rodded' appearance (Fig. 126) 

 We shall see directly that this morphological agreement is the 

 index of a functional likeness. The blood-supply of the tubules, 

 especially of the convoluted portions, is exceedingly rich, 

 the efferent vessels of the glomeruli breaking up around them, 





