1332 



THE UKO-GEOTTAL SYSTEM. 



Bladder 

 / 



Large intestine 

 I Wolfflan duct 



Pelvis of kidney 



THE BLADDER. 



The main portion of the bladder is formed from the superior (cephalic) part of the 

 anterior subdivision of the cloaca. This at an early time becomes flattened dorso-ventrally, 

 and produced laterally into two horn-like projections in the region where the Wolffian 



ducts open (Fig. 1043). Inferiorly 



Aiiantois it becomes constricted to form the 



uro-genital canal. Little by little 

 the lower ends of the Wolffian ducts 

 open out and are absorbed into the 

 wall of the developing bladder, and 

 soon it comes about that the ureters, 

 which originally were outgrowths 

 of the Wolffian ducts, open directly 

 into the bladder. The openings 

 of the ureters become shifted latter- 

 ally, but the final position of the 

 openings of the Wolffian ducts is 

 close to the median plane in the 

 upper prostatic part of the urethra. 

 The bladder has therefore a double 

 origin : its main portion is derived 

 from the entodermal cloaca ; its 

 smaller basal part arises from the 

 opened-out lower ends of the Wolffian 

 The cloaca is becoming separated into rectal and uro-genital ducts. The latter portion approxi- 

 portions by the formation of the septum recto- urethrale. rnatp i v oorrpsrirmr l, to thp triovm 

 The ureter has acquired a separate opening into the anterior matel 7 corresponds 

 division of the cloaca. (Drawn from a model constructed VCSlCSe of the adult, and must 

 by Prof. F. Keibel. ) be regarded as having its source 



from the mesoderm. The extreme 



cephalic end of the anterior part of the cloaca tapers gradually, and beyond the umbilicus 

 is continuous with the allantois. This part of the cloaca loses its lumen about the fifth 

 week, and from it is derived the fibrous cord of the urachus or median umbilical ligament, 

 which in the adult reaches from the bladder apex to the umbilicus. 



The cavity of the urachus is sometimes not lost so early, and in rare cases it has been 

 found persisting in the child or adult as a pervious channel extending from the apex of 

 the bladder to the umbilicus. Here it may open on the surface of the body. 



THE MALE URETHRA. 

 The first part of the male urethra has an origin similar to that of the basal part of 



Cloacf 



Ureter 

 Septum recto-urethra le 



FIG. 1043. TAIL END OF HUMAN EMBRYO ABOUT 33 DAYS OLD. 



Ureter 



Wolfflan duct 

 Rectum j 



Miillerian ducts \ , 



Bladder \ 



Symphysis pubi 



[/ ' 



Vertebra (body) 



i Neural tube 



V 1 S 



Urino-genital canal , \l 

 Clitoris * 



Notochord 



FIG. 1044. TAIL END OF FEMALE HUMAN EMBRYO ABOUT 9 WEEKS OLD. 



The rectum has acquired an opening and the entoderm of the uro-genital canal is continued into the genital 

 eminence (clitoris). (Drawn from a model constructed by Prof. F. Keibel. ) 



