THE KIDNEYS 473 



Structure. — The surface of the kichiey is covered by a thin but stronp; fibrous 

 capsule (Tunica fibrosa), which is in general easily stripped off the healthy kidney. 

 It is continued along the hilus and lines the renal sinus. Sections through the 

 kidney show it to consist of an external cortical substance and an internal medullary 

 substance.^ The cortical substance (Substantia corticalis) is red brown in color 

 and has a granular a])pearance. It is dotted over with minute dark points; these 

 are the renal (or Alalpighian) corpuscles (Corpuscula renis), each consisting of the 

 dilated origin of a uriniferous tul)ule (Capsula glomeruli), with an invaginated tuft 

 of capillaries (Glomerulus) inclosed by it. The medullary substance (Suljstantia 

 moduUaris) is more resistant and presents a distinct radial striation. Its central 

 part is pale, but its periphery, the intermediate zone, is of a deep red color; in 

 the latter are seen, at fairly regular intervals, sections of the relatively large arci- 

 form vessels, which are taken to represent the demarcation between the i)rimitive 

 lobes." Between the vessels the medulla is prolonged somewhat toward the per- 

 iphery, forming the bases of the renal (or Malpighian) pyramids. These are not 

 very pronounced in the kidney of the horse, especially as the gland is not papillated. 



Renal crest I 'i Iris Renal Branches Ureter 



vein of renal artery 



Fig. 379. — Tr.\nsverse Section' of Right Kidxey of Horse Through the Hilus. 

 Posterioi' portion of organ hardened in situ. Note curvature of dorsal surface. 



Between the bases of the pyramids processes of the cortex dip in toward the sinus,, 

 forming the renal columns.^ The inner central part of the medulla forms a concave 

 ridge or crest which projects into the pelvis of the kidney; the crest is marked by 

 numerous small openings at which the renal tubules terminate. 



Examination with a pocket lens shows that the cortex is imperfectly divided 

 into lobules (Lobuli corticales). Each lobule consists of an axial radiate part (Pars 

 radiata), surrounded by a convoluted part (Pars convoluta). The former (formerly 

 termed pyramids of Ferrein) apjiear as ray-like prolongations from the bases of 

 the pyramids (hence also termed medullary rays), and consist largely of narrow, 

 straight or slightly flexuous, tubules (limbs of the loops of Henle). The convoluted 

 part (formerly termed the labyrinth) is granular in appearance, and consists largely 

 of the renal corpuscles and convoluted tubules. 



The pelvis of the kidney (Pelvis renalis) is the dilated origin of the excretory 



' The most instructive sections are those made in tlie horizontal and transverse planes, 

 through the pelvis in each case. * 



- The foetal kidney is divided by furrows into a number of polygonal areas, each of which 

 is the base of a pyramidal lobe or renculus. These furrows usually disappear before or soon after 

 birth in the foal, although traces of them are sometimes seen in the adult. 



•^ In the kidney of the horse the renal columns dip in between the pyramids very super- 

 ficially as compared with the arrangement in the human kidney. Breuer states that the pyra- 

 mids are 40 to 64 in number, and are arranged in four rows. Only the middle ones are distinct. 



