THE KIDNEYS 557 
pancreas. The medial border is longer, straighter, and thicker than that of the 
right kidney. 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 czecus 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 cases 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 the three areas of the dorsal surface are often dis- 
tinet. The psoas area (Impressio muscularis) is flat, parallel with the medial border, and widens 
behind. The diaphragmatic area is small and convex; it is erescentic and is confined 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 kidneys 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 crest 
Acce SSOTY -~ 3 
renal 
artery 
1 
: Renal artery 
Ureter 
Fic. 498.—Frontat (Horizontat) Section oF Krpney or Horse. 
The renal vein is 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.!. On account of its relations 
with the liver, pancreas, and base of the cecum, 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- 
jborn foal the kidney weighs about 6 ounces (ca. 170 gm.). 
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| _ 1The amount of perirenal fat varies; in animals in good condition it may entirely conceal the 
pteys; in such cases the impressions produced by contact of the kidney with contiguous struc- 
tures may be indistinct. 
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