1248 UROGENITAL SYSTEM 



is capped by a thin layer of cortex. Such a condition is permanent in some of the lower animals; 

 but in man the superficial indications of morphological segmentation usually become obliterated 

 during the progress of growth of the cortical tissue, and are seldom visible after the age of ten. 



Development. — In the development of the embryo, representatives of three different sets 

 of excretory organs occur, the permanent kidney (metanephros) being the last to form. The 

 two earlier sets (pronepliros and mesonephros) have a common duct, the Wolffian duct, and 

 from the lower end of this an outgrowth develops, which extends upward on the posterior 

 abdominal wall and comes into connection with a mass of embryonic tissue known as the 

 metanephric blastema. The outgrowth gives rise to the ureter, pelvis and collecting tubules, 

 while the remaining portions of the tubules are formed from the blastema. 



Various abnormalities may result from modifications of the development of the kidneys. 

 (1) Occasionally the ureteric outgrowth of one side fails to develop, the result being the occur- 

 rence of a single kidney. (2) The blastema may fail to attain its normal position, in which 

 case the kidney may be situated in the iliac region or even in the pelvis; or the blastema may be 

 drawn into an unusual position, the kidney resting on the vertebral column, or even on the 

 opposite side of the abdomen; (3) or the two blastemas may fuse to a greater or less extent, 

 forming a "horse-shoe kidney," extending across the vertebral column; or, if the fusion be more 

 extensive, an apparently single kidney, which may rest upon the vertebral column, or to one 

 side of it. Such fused kidneys may be distinguished from single kidneys by the fact that they 

 possess two ureters opening normally into the bladder. (4) In rare cases, a blastema may be- 

 come divided, an accessory kidney of varying size being thus produced. (5) Finally, in one or 

 more of the tubules there may be a failure of the union of the portion derived from the blas- 

 tema with the collecting tubule derived from the ureteric upgrowth, and the secretion having 

 no means of escape from such malformed tubules, they become greatly dilated, producing a 

 cystic kidney. 



THE URETERS 



The ureter (figs. 1004, 1007, 1012, 1015), which serves as the excretory duct 

 of the kidney, is a canal, expanded and irregularly branched above, but narrow 

 and of fairly uniform dimensions throughout the rest of its course. At its origin 

 in the renal sinus it consists of a number of short tubes, usually eight or nine, called 

 calyces minores (fig. 1012), each of which embraces a renal papilla, or occasionally 

 two papillae may be connected with a single calyx. These calyces minores open 

 directly or by means of short intermediate tubes (infundibula) into two short 

 passages, the superior and inferior calyces majores, which in turn unite after a 

 longer or shorter course to form the pelvis. Occasionally a third or middle calyx 

 major is present. 



The pelvis [pelvis renahs] (fig. 1012) is usually more or less funnel-shaped, 

 being wider above, where it Hes between the two lips of the hilus, and narrower 

 below, where it arches downward and medially to become continuous with the 

 ureter proper. It is, however, very variable in shape and in some cases is hardly 

 larger than the ureter. Usually it is flattened dorso-ventrally so that its anterior 

 and posterior walls are in contact and its cavity represented merely by a fissure. 

 The majority of the branches of the renal vein and artery lie in front of it, im- 

 bedded in fat tissue, and anterior to these are the descending portion of the duo- 

 denum on the right side and the pancreas on the left. The intra-renal portions of 

 the ducts, including the pelvis, are considered parts of the kidney. 



The ureter proper (fig. 1007) extends from the termination of the pelvis to the 

 bladder, its course lying in the subperitoneal tissue. It is a tube about 5 mm. in 

 diameter when distended and it is fairly uniform in size, except that a slight con- 

 striction occurs where it enters the pelvis and a second one occurs at about the 

 middle of its abdominal portion. Its length is variously stated, but the average 

 in the male adult may be taken as about 30 cm., the right being usually a little 

 the shorter. 



Course and relations. — The course of each ureter may be conveniently divided 

 into tliro(! portions, abdominal, pelvic, and vesical. The abdominal portion 

 [pars alKloininalis] runs downward and slightly medially and is in relation pos- 

 teriorly with the psoas muscle and its fascia; it crosses the genito-femoral nerve 

 obliquely and in the lower part of its course passes in front of the common iliac 

 artery near its bifurcation. Anteriorly it is covered by peritoneum and is crossed 

 by the spermatic or ovarian vessels. Medially it is in relation on the right side 

 with the inferior vena cava and on the left with the aorta, the vein being almost 

 in contact with tlie right ureter, while the artery is separated from the left one 

 by an interval that (lirainishes from 2.5 cm. above, to 1.5 cm. opposite the 

 bifurcation of tlie vessel. 



'IMie pelvic portion [pars pelvina] passes in front of the sacro-iliac articulation 



