STUUCTURE OF THE KIDNEYS. 403 



muscle ; and, lastly, on the psoas muscle. The external lorder, convex 

 in its genei'al outline, is directed somewhat backwards towards the wall 

 of the abdomen. The inierneil horcJer, concave and deeply excavated 

 towards the middle, is directed a little downwards and forwards. It 

 presents a longitudinal fissure bounded by an anterior and posterior 

 lip, and named the Jiihis of the hidneij, at which the vessels, the excre- 

 tory 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 -^j^vjww 

 excretory duct or ureter behind and towards the lower part. The v \ 

 iijjpcr end of the kidne}', which is larger than the lower, is thick ^V>-^— 

 and rounded, and supports the suprarenal capsule, which descends a 'racA.o^ 

 little way upon its anterior surface. This end of the kidney reaches, on w jv 1 1 

 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 in- 

 wards, 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 the 

 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 rela- 

 tive size, and number. Thus, they are sometimes foimd longer and nan-ower, 

 and sometimes 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 the two kidneys are joined by 

 their lower ends across the front of the great blood-vessels and vertebral column. 

 The conjunct organ has usually the form of a semiciixle, the concavity of which 

 is directed upwards — hence the appellation of the Jwrse-ishoe 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 three glandular masses have been found, the super- 

 numeraiy organ being placed either in front or on one side of the vertebral 

 column, or in the pelvic cavity. 



Obvious Structure. — The kidney is surrounded by a proper fibrous 

 coat, which forms a thin, smooth, but firm investment, closely covering 

 the organ. It consists of dense fibro-areolar tissue, together with nu- 

 merous fine elastic fibres, and can easily be detached from the substance 

 of the gland, to which it adheres by minute processes of connective 

 tissue and vessels. 



On splitting open the kidney by a longitudinal section, from its 

 outer to its inner border, the fissure named the hilus (fig. 286, h, h) is 

 found to extend some distance into the interior of the organ, forming a 

 cavity called the sinus of the kidney (s). This is enclosed on all sides 

 except at the hilus by the solid substance of the organ ; and is lined 

 by an inward prolongation of the fibrous coat. The solid part consists 

 of a cortical and a meclullary substance ; the latter being arranged 

 in separate conical masses named " pyramids of Malpighi," with their 

 broad bases (&, I) directed towards*^ the surface, and their points 

 towards the sinus, where they form prominent iMiyilkc. The pyramids 

 are imbedded in the cortical substance, which separates them from each 

 other, and encloses them everywhere except at the papilla, Avhich 

 emerge from it and project into the sinus. 



