THE KIDNEYS 



557 



pancreas. The medial border is longer, straighter, and thicker than that of the 

 right Ividney. It is related to the posterior aorta, the adrenal, and the ureter. The 

 lateral border is related chiefly to the base of the spleen. The anterior extremity 

 extends almost to the saccus caecus of the stomach; it is related to the left end of 

 the pancreas and the splenic vessels. The posterior extremity is usually larger 

 than the anterior one. 



The form of the left kidney is variable. In some eases its outline is similar to that of the 

 right kidney, but its ventral surface is convex and is often marked by several furrows which diverge ' 

 from the hilus. In well-hardened specimens tlie three areas of the dorsal surface are often dis- 

 tinct. The psoas area (Impressio muscularis) is flat, parallel with the medial border, and widens 

 behind. The diaphragmatic area is small and convex; it is crescentic and is confuied to the an- 

 terior end. The lateral splenic area is somewhat flattened and is often so extensive and distinct 

 as really to constitute a third surface as in Fig. 496. 



Fixation. — The kitlneys are held in position chiefly by the pressure of adjacent 

 organs and by the renal fascia. The latter is a special development of the sub- 



Renal cre^t 



I )U( j' '• ''' liinre 



Medullary substance 



Accessory - 

 renal 

 artery 



Renal artery 



Ureter 



Fig. 498. — Frontal (Horizontal) Section of Kidney of Horse. 

 The renal vein ig removed. A large accessory renal artery entered the posterior pole. Sections of arteries in limiting 

 layer between cortical and medullary substance are white in figure. 



peritoneal tissue, which splits into two layers to enclose the kidney, together with 

 the perirenal fat, which is termed the capsula adiposa.i On account of its relations 

 with the liver, pancreas, and base of the caecum, the right kidney is much more, 

 strongly attached than the left one. It is, therefore, not surprising that the latter 

 varies somewhat in position; its posterior extremity may be ventral to the third or 

 fourth lumbar transverse process. The position of the right kidney, excluding its 

 movements during respiration, seems to be very constant. 



"Weight and Size. — The right kidney is usually one or two ounces heavier than 

 the left. The average weight of the right kidney is about 23 to 24 ounces (ca. 

 700 gm.); that of the left, about 22 to 23 ounces (ca. 670 gm.). The relation of 

 the weight of both kidneys to the body-weight is about 1 : 300-350. In the new- 

 born foal the kidney weighs about 6 ounces (ca. 170 gm.). 



1 The amount of perirenal fat varies ; in animals in good condition it may entirely conceal the 

 kidneys; in such cases the impressions produced by contact of the kidney with contiguous struc- 

 tures may be indistinct. 



