FORM AND TOSTTION OF THE KIDNEYS. 927 



equal weight, the left being almost always heavier than the right. The difference, 

 according to Rayer, is equal to about one-sixth of an ounce. The actual average 

 difference was found by Reid in ninety-three cases (male and female), to be rather 

 more than one-fourth of an ounce. The proportionate weight of the two kidneys to 

 the body is about 1 to 240. 



The specific gravity of the renal substance is, on an average, T052. 



^ 



The surface of the kidney is smooth and has a deep red colour. Its form, 

 is peculiar : it is compressed before and behind, convex on its outer and 

 concave on its inner border, and somewhat enlarged at its upper and lower 

 ends. 



The anterior surface, more convex than the posterior, is directed some- 

 what outwards, and is partially covered at its upper end by the peritoneum, 

 which is separated from it lower down by loose areolar tissue. The duo- 

 denum and ascending colon, both destitute of peritoneum behind, are in 

 contact with the anterior surface of the right kidney, and the descending 

 colon with that of the left. The front of the right kidney, moreover, 

 touches the under surface of the liver, and that of the left the lower ex- 

 tremity of the spleen. The posterior surface, natter than the anterior, and 

 imbedded in areolar tissue, rests partly upon the corresponding pillar of the 

 diaphragm, in front of the eleventh and twelfth ribs; partly on the anterior 

 layer of the lumbar fascia, covering the quadratus lumborum muscle ; and, 

 lastly, on the psoas muscle. The external border, convex in its general 

 outline, is directed outwards and backwards towards the wall of the abdo- 

 men. The internal border, concave and deeply excavated towards the 

 middle, is directed a little downwards and forwards. It presents in its 

 middle a longitudinal fissure bounded by an anterior and posterior lip, and 

 named the hilus of the kidney, at which the vessels, the excretory duct, and 

 the nerves enter or pass out. In this hilus, the renal vein lies in front, the 

 artery and its branches next, and the expanded excretory duct or ureter 

 behind and towards the lower part of the hilus. The upper end of the 

 kidney, which is larger than the lower, is thick and rounded, and supports 

 the suprarenal capsule, which descends a little way upon its anterior sur- 

 face. This end of the kidney reaches, on the left side, to about the upper 

 border of the eleventh rib, and, on the right, half a rib's breadth lower. It 

 is moreover directed slightly inwards, so that the upper ends of the two 

 kidneys are nearer to each other than the lower ends, which are smaller and 

 somewhat flattened, diverge slightly from the spine, and reach nearly as low 

 as the crest of the ilium. It may here be remarked that, by placing the 

 larger end of a kidney upwards and its flatter surface backwards, or by 

 noticing the relation of the parts in the hilus, the side of the body to which 

 the organ belongs may be determined. 



Varieties, The kidneys present varieties in form, position, absolute and relative 

 size, and number. Thus, they are sometimes found longer and narrower, and some- 

 times shorter and more rounded than usual. Occasionally one kidney is very small, 

 whilst the other is proportionately enlarged. The kidneys may, one or both, be 

 situated lower down than usual, even in the pelvis. 



Instances are now and then met with in which only one kidney is present, the single 

 organ being sometimes, though not always, formed by the apparent junction of the 

 two kidneys across the front of the great blood-vessels and vertebral column. The 

 united organ has usually the form of a crescent, the concavitj of which is directed 

 upwards, hence the appellation of the horse-shoe kidney. Sometimes two united 

 kidneys are situated on one or other side of the vertebral column, in the lumbar 

 region, or, but much more rarely, in the cavity of the pelvis. In other very rare cases, 



