558 THE URINARY ORGANS OF THE HORSE 
Chauveau gives as an average 750 grams for the right kidney and 710 grams for the left. 
Ellenberger and Baum (24 cases) give the right kidney as varying between 430 and 840 grams; 
and the left between 425 and 780; this is an average of 635 grams (about 22'% ounces) for the 
right kidney, and 602.5 grams (about 211% ounces) for the left. They give the relation of the 
weight of both kidneys to the body-weight as 1: 255-344. Ina Percheron mare weighing about 
2000 pounds the right kidney weighed 4 pounds 3 ounces, and the left one 4 pounds. In a horse 
of medium size the right kidney is about six inches (ca. 15 em.) in length, about the same in width, 
and about two inches (ea. 5 em.) thick. The left kidney is about seven inches (ca. 18 em.) long, 
four to five inches (ca. 10 to 12 em.) wide, and two to two and a half inches (ca. 5 to 6 cm.) thick. 
Structure.—The surface of the kidney is covered by a thin but strong fibrous 
capsule (Tunica fibrosa), which is in general easily stripped off the healthy kidney; 
it is continued into the renal sinus, where it is attached. 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 appearance. It is dotted over with minute dark points; these 
are the renal corpuscles (Corpuscula renis),' each consisting of the dilated origin of 
a uriniferous tubule (Capsula glomeruli), with an invaginated tuft of capillaries 
(Glomerulus) enclosed by it. The medullary substance (Substantia medullaris) 
Renal crest Pelvis Renal Branches Ureter 
vein of renal artery 
Fic. 499.—TRransverse Section or Ricutr Kipnery or Horse Passtne THrouGH THE HiLus. 
Posterior portion of organ hardened in situ. Note curvature of dorsal surface. 
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 arciform vessels, 
which are taken to represent the demarcation between the primitive lobes.?  Be- 
tween the vessels the medulla is prolonged somewhat toward the periphery, forming 
the bases of the renal pyramids (Pyramides renales). These are not very pro- 
nounced in the kidney of the horse, especially as the gland is not papillated. Be- 
tween the bases of the pyramids processes of the cortex dip in toward the sinus, 
forming the renal columns (Column renales).* The inner central part of the 
medulla forms a concave ridge which projects into the pelvis of the kidney. This 
projection is termed the renal crest; it presents numerous small openings at which 
renal tubules open into the pelvis of the kidney, and hence the surface here is known 
as the area cribrosa. 
1 Also known as Malpighian corpuscles. 
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2 The feetal 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. 
3In the kidney of the horse the renal columns dip in between the pyramids very superficially | 
as compared with the arrangement in the human kidney. Breuer states that the pyramids are | 
40 to 64 in number, and are arranged in four rows. Only the middle ones are distinct. | 
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