THE KIDNEYS. 



487 



PROPER TISSUE. The glandular tissue of the kidneys (areola parenchyma 

 or matrix) has, externally, a reddish-brown colour, more or less deep in 

 different individuals. It is dense and friable, and easily torn when deprived 

 of its fibrous capsule. Its substance is not everywhere homogeneous : very 

 dark-coloured externally, where it forms the cortical layer, it becomes 

 whiter around the pelvis, where it consitutes the medullary layer ; where the 

 latter comes in contact with the former, and sometimes even near the pelvis, 

 it assumes a tint like that of wine. 



These two portions are not well defined, but penetrate each other 

 reciprocally, so as to compose, at their point of junction, irregular festoons, 

 very readily perceived in a horizontal section of the kidney (Fig. 248). 



The cortical is also distinguished from the medullary substance by its 

 granular aspect, and the presence of minute, reddish spheres, readily visible 

 to the naked eye, and named Malpighian corpuscles ; while the medullary 

 substance appears composed of radiating fibres. 



Fig. 248. 



HORIZONTAL LONGITUDINAL SECTION OP THE HORSE'S KIDNEY. 



a, Cortical (or vascular) portion; 6, Medullary (or tubular) portion; c, Peripheral 

 portion of the latter ; d, Interior of the pelvis ; d', d', Arms of the pelvis ; e 

 Border of the crest ; /, Infundibulura ; g, Ureter. 



In the Horse, the tissue of the kidney cannot be divided into lobules or 

 pyramids ; to the naked eye it appears to be composed of fibres that start 

 from every part of its exterior, and converge towards the crest of the pelvis. 

 A microscopical examination demonstrates these fibres to be canals or tubes ; 

 hence they are designated tubuli uriniferi or Bellini s tubes. A delicate 

 connective tissue, a kind of stroma, which is very rare in the cortical, but 

 more abundant in the medullary substance, especially in the vicinity of the 

 pelvis, sustains the vessels and nerves, and unites the tubuli uriniferi to each 

 other. 



The tubuli uriniferi are constituted by a proper amorphous membrane, 

 very thin and elastic, whose internal face is lined by simple epithelium that 

 readily alters ; the cells are polygonal in certain points, polyhedral in others, 

 and transparent or granular 



