THE KIDNEY. 



207 



Proximal 



convoluted 



tubule 



Intermediate 

 tubule (distal 

 convoluted) 



Intermediate 



tubule 



Efferent 



vessel 



Neck 



Afferent 



vessel 



Capsule 



Interlobular 



artery 



Descending 

 limb 



Ascending 

 limb 



numerous but larger, in consequence of repeated union, until, as the wide 

 papillary ducts, they end at the summit of the renal papilla. 



The Kidney-Substance. The fundamental components of the ver- 

 tebrate excretory organ, both in the foetal and mature condition, include: 



(1) a tuft of arterial capillaries derived more or less directly from the aorta; 



(2) tubules lined with secretory epithelium; and (3) a duct for conveying 

 the excretory products. 



These COnStitUentS are Labyrinth Med. ray Labyrinth 



represented in the kidney 

 of man and the higher an- 

 imals by: (i) the glomer- 

 ulus, (2) the convoluted 

 uriniferous tubules, and 



(3) the collecting tubules 

 and the ureter composing 

 the duct-system. Since, 

 in a general way, to the 

 epithelium may be as- 

 cribed the function of tak- 

 ing from the circulation 

 the more solid constitu- 

 ents of the urine, and to 

 the glomerulus the secre- 

 tion of the watery parts, 

 obviously the most favor- 

 able arrangement to se- 

 cure the removal of the 

 excretory products is one 

 insuring flushing of the 

 entire tubule with the fluid 

 secreted by the glomeru- 

 lus. Such an arrangement 

 implies the location of the 

 vascular tuft at the very 

 beginning of the tubule 

 a disposition which in fact 

 is found in the kidneys of 

 all higher animals. The 

 number of the glomeru- 

 li, therefore, corresponds 

 with that of the urinifer- 

 ous tubules, each of which 

 begins in close relation 



with a vascular tuft. The kidney-substance consists of an intricate, although 

 definitely arranged, complex of uriniferous tubules, supported by an inter- 

 stitial connective tissue stroma, which have their commencement in the cortex 

 and their termination at the apices of the papillae, their intervening course 

 being marked by many and conspicuous variations in the character, size, and 

 direction of the tubules. 



The uriniferous tubule begins as a greatly expanded blind extremity, 

 the capsule (i), which surrounds the vascular tuft or glomerulus, the two 

 together constituting the Malpighian body or renal corpuscle, which lies 

 within the labyrinth. On leaving the Malpighian body, the tubule becomes 



Loop 

 Henle 



Papillary duct 



Papilla 

 FIG. 255. Diagram illustrating the course of a uriniferous tubule. 



