1010 THE URIXARY ORGAXS 



The cuter border of the kidney reaches u jioint about three and a half or four 

 inches external to the lumbar spinous processes. On the right side, it is in contact 

 with the liver in its upjier lialf or two-thirds; on the left, its upper third or half 

 rests against the renal groove in the posterior portion of the visceral surface of the 

 spleen. 



The inner border of the right kidnw apjtroaches very close to the vena cava, 

 especially above; that of the left is divided from the aorta by an interval of an incli 

 or more. 



The position of the kidne3'S at the l)ack of the al)dominal cavity involves a cer- 

 tain amount of pressure upon the organs and their vessels and nerves by the weight 

 of the viscera in front Avhen the body is supine, and there is reason, to believe that 

 their secretory functions are consequently influenced by changes of posture to an 

 extent that may be utilised in therapeutics. 



The structures lying within the sinus are the renal artery and vein, the renal 

 lym|)haties (ves.'^els and glands ), a plexus C)f nerves, the duct, and more or less con- 

 nective and adipose tissue continuous with the fatty capsule. The renal artery is 

 a branch of the aorta given off opposite the first lumbar vertebra and behind the 

 pancreas. On reaching the hilum it usually breaks up into four branches, three of 

 which pass in front of the pelvis to supply the superior, middle, and inferior zones 

 of the organ, while a fourth runs behind the pelvis close to the posterior lip of the 

 hilum and is distributed over the lower half or two-thirds. This may be wounded 

 in an attempt to remove a calculus b}^ incision of the posterior wall of the pelvis. 

 Besides these, irregular vessels may lAerce the gland above or below the hilum 

 (fig. 607). The left renal vein receives the spermatic or utero-ovarian vein, and is 

 usually somewhat lower than the right. The shortness of the right renal rein should 

 be remembered in the operation of nephrectomy. 



Structure. — The kidney Avhen removed from its fatty investment is seen as a 

 yellowish-red organ covered b}^ a thin but strong fibrous capsule (tunica propria), 

 which is prolonged through the hilum into the sinus, where it becomes continuous 

 with the sheaths of the renal vessels, and extends as far as the attachments of the 

 suljdivisions of the duct around the renal papillse. The whole capsule may be easily 

 peeled off from the healthy kidney, except at the bottom of the sinus, where it is 

 fixed 1)y the vessels and duct; and as the capsular vessels are of small size, the 

 process of stripping is attended with little hsemorrhage when practised in the coui'se 

 of operations upon the living suljject. 



On section through the kidney, its substance is found to comprise an external 

 or cortical and an inner or medullary segment. The medulla consists of a variable 

 numl)er (eight to eighteen) of conical segments called pyramids of Malpighi, the 

 apices of which project into the bottom of the sinus (fig. 609) and are surrounded 

 by the primary segments (calices) of the duct, while their l:)ases are turned towards 

 the surface, but are separated from it and from each other by the cortex. The 

 pyramids average in their axial diameter about three-quarters of an inch, and have 

 a width at the liase of about two-thirds of an inch (16 mm.). They are smooth 

 and somewhat glistening in section, and marked with delicate strife which converge 

 from base to apex, and indicate the course of the uriniferous tubules. The blunted 

 apex, or papilla, single or blended with one or even two of its fellows, is embraced 

 by a calyx, and if examined with a hand lens will be seen to present a varial)le 

 number (twelve to eighty) of minute apertures, the foramina papillaria, through 

 which the secretion escapes into the duct. 



The cortex may be divided into two portions: a peripheral layer, the cortex 

 proper, whieh is a little less than half an inch (12 mm.) in thickness, and extends 

 from the cajjside to the leases of the ])yramids of Malpighi; and processes called 

 columns of Bertin, which dip inwards between the Malpighian pyramids to reach 

 the bottom of the sinus, where they are covered by the fil)rous capsule and more or 

 less adipose tissue {[\^. 613). In section the cortex is somewhat granular in aspect, 

 and in an injected kidney is seen to be dotted with minute points corresi)onding to 

 vascular glomeruli lying within the cajcal origin of the uriniferous tubules (capsules 

 of BoAvman). Examined more closely, it displays a number of small pyramidal 

 groups of tubules, some l:)elonging to the cortex proper, with their bases resting uj^on 

 the bases of the Malpighian pyramids, the apices directed towards, but not reaching, 



