THE KIDNEYS. 



1875 



Fig. 1596. 



Area still 

 covered by 

 fibrous cap- 

 sule, exter- 

 nal surface 

 of which is 

 roughened 

 by strands 

 of connec- 

 tive tissue 



y' Renal 

 / artery 



takes in approximately the median half of the interior of the organ. The greatest 

 dimension of the sinus corresponds with the long axis of the kidney, the shortest with 

 the distance between the anterior and posterior walls. The space — most extended 

 vertically — is compressed from before backward, while its greatest depth (2. 5-3. 5 cm. ) 

 is just above the upper border of the hilum. The sinus is occupied in large measure 

 by the dilated upper end of the ureter, the renal pelvis, and its subdivisions, the 

 calyces: the remaining space accommodates the blood-vessels, lymphatics, and nerves 

 that pass through the hilum and the intervening cushion of areolar and adipose tissue 

 continuous with the perirenal fatty capsule. The fibrous capsule of the kidney covers 

 the rounded lips of the hilum and is continued into the sinus, to which it furnishes 

 a partial lining. 



In contrast to the even external surface of the kidney, the walls of the sinus are 

 beset with conical elevations, the renal papillce, which are well seen, however, only 

 after removal of the contents and the fibrous lining of the sinus. The papillae mark 

 the apices of the pyramidal masses of kidney-tissue of which the organ is composed. 

 The individual cones, from 7 to 10 mm. in 

 height, are in many instances somewhat com- 

 pressed, so that their bases are elliptical in 

 section instead of circular. Adjacent ones 

 may undergo more or less complete fusion, 

 the resulting compound papillae being often 

 grooved and irregular in form. Usually from 

 eight to ten papillae are present in each kid- 

 ney, but their number varies greatly, as few 

 as four and as many as eighteen having been 

 observed (Henle). The walls of the sinus 

 between the bases of the papillae are broken 

 up into elevations and depressed areas, the 

 latter marking the localities at which the 

 blood-vessels and nerves enter and leave the 

 renal substance. The apex of each papilla 

 is pierced by a number of minute openings, 

 barely recognizable with the unaided eye, 

 which mark the terminal orifices (foramina 

 papillaria) of the uriniferous tubules from 

 which the urine escapes from the renal tissue 

 into the receptacles formed by the calyces 

 which surround the papillae and are attached 

 to their bases. The number of uriniferous tu- 

 bules opening at the apex of a single papilla — 

 the field in which the pores open being the 



area cribrosa — varies with the size of the cone, from eighteen to twenty-four being 

 the usual complement for a simple papilla. When the latter is compound and of 

 large size, more than twice as many orifices may be present. 



Architecture of the Kidney. — The entire organ — a conspicuous example of 

 a compound tubular gland — is made up of a number of divisions which in the mature 

 condition are so closely blended as to give little evidence of the striking lobulation 

 marking the fcetal kidney. The external surface of the latter (Fig. 1597) is broken 

 up by furrows into a number of irregular polygonal areas, each representing the 

 base of a pyramidal mass of renal tissue, the kidney lobe or renculus, which, sep- 

 arated from its neighbors by an envelope of connective tissue, includes the entire 

 thickness of the organ between its exterior and the sinus, a renal papilla being the 

 apex. For a short time after birth the lobulation is evident, but later the de- 

 marcations gradually disappear from the surface, which becomes smooth, and the 

 interlobular connective-tissue septa within the organ disappear, the pyramids alone 

 indicating the original lobulation. 



Renal 

 vein 

 Renal pel- 

 vis, lower 

 part 



Ureter 



Anterior surface of right kidney from which 

 fibrous capsule has been partly removed ; blood- 

 vessels and renal duct are seen entering and emerging 

 through hilum. 



Although evidences of the latter occasionally persist in the adult human organ, the kidneys 

 of many of the lower animals (reptiles, birds, ruminants, cetaceans, and certain camivora) retain 



