108 



HUMAN EMBRYOLOGY AND MORPHOLOGY. 



they become functionless ' and only of pathological importance 

 Their presence in the female is due to their being inherited from 

 the male. 



THE KIDNEY. 



Origin of the Permanent Kidney. — In Fishes and Amphibians 

 the Wolffian body alone acts as a kidney. In Reptiles, Birds 

 and Mammals, the permanent or hind kidney appears and 

 supplants the Wolffian kidney. The kidney appears in the 

 human embryo at the beginning of the second month. It arises 



Wolffian duct. 



allantois 



genital, tub. 



cloaca. 



genital gl. 



renal mesoblast 



renal bud 

 rectum 



cloacal membs 

 cauda- 



Fig. S3. — The Origin of the Renal Bud (diagrammatic). 



(see Fig. 83) as a bud from the dorsal side of the Wolffian duct 

 near the termination of that duct in the cloaca. At first it is i 

 stalked bud with a narrow lumen ; it rapidly extends forwards t( 

 the lumbar region behind the Wolffian body and behind th< 

 peritoneum. The stalk of the bud forms the ureter. Th< 

 connection of the stalk with the Wolffian duct is lost ; the ter 

 mination of the ureter migrates along the duct until it reachei 

 that part of the cloaca which afterwards forms the bladder (Fig 

 84). The dilated cephalic end of the bud divides into severa 

 secondary buds. The dilated terminal part forms tb 

 pelvis of the kidney, its infundibula and calyces. The tubule 



