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 42o and 7S0; this is an average of 635 grams (about 22 J 2 ounces) for the 

 right kidney, and 602.5 grams (about 21}^ oimces) for the left. They give the relation of the 

 weight of both kidneys to the body-weight as 1 : 255-344. In a 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 sLx inches (ca. 15 cm.) in length, about the same in width, 

 and about two inches (ca. 5 cm.) thick. The left kidney is about seven inches (ca. 18 cm.) long, 

 four to five inches (ca. 10 to 12 cm.) wide, and two to two and a hah 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 corticahs) 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 



4 



Pelns 



Renal Branches Ureter 

 rem of renal artery 



Fig. 499. — Tr.insvehse Section of Right Kidney op Horse Passing 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 (Columnse 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. 



' Also known as Malpighian corpuscles. 



^The fa'tal kidney is divided by furrows into a number of polygonal areas, each of which 

 is the base of a pyramidal lobe or reniculus. 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 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. 



