DEVELOPMENT OF GEXITO-VRiyARY OROAXS 



lOoo 



DEVELOPMENT OF THE GENITOURINARY ORGANS 



There is at first a periud in tlic f^rovvtli uf the oiuhryo duriii;,' which there is no iixlication of 

 any iirovision either for the irenerative or for tlie urinary luuction. A little later tlie rudiments 

 of a genito-urinary ajjparatus are laid down, but there is as yet no ai)i)c'aranee oi" sexual differen- 

 tiation. Finally, a third stage in the fomative process is occupied by the evolution of the orL'ans 

 characteristie of the masculine or feminine type, and the completion of the glandular and otlier 

 structures, which provide for the secretion, storage, and ultimate expulsion of the urine I'rom the 

 body. It will be seen that in the eour.se ofthe.se devclo]imental changes certain of the .structures 

 concerned appear and a.><sunie their i)ermanent characters gradually and without alteration of 

 plan; others, oiiginally employed lor i)urposes unconnected with "the genito-urinary system, 

 become adapted to take their place in this section of the economy ; others belonging to the .system 

 from the first are brought into a special condition of i'unctional activity only to undergo conversion 

 to a different use later on ; while others again may, according to the sex a.s.sumed by the foetus, 

 either dwindle into u.selcss relics without ever taking any share in the W(jrk of the body, or may 

 become el:\borated into important and tfficient parts oi' the repntductive organism. 



Fig. 644.— Diagram of the Primitive Gexito-ukixaky Organs before 

 DiFFBKEXTlATiON OF Sex. (After Heule.) 



MULLER'S DUCT 

 GENITAL GLAND 

 WOLFFIAN BODY 



(Tubular structure not shown) 



Hound ligament 



WOLFFIAN DUCT 



UNITED MULLERIAN DUCTS 

 OPENINGS OF WOLFFIAN DUCT 



SINUS URO-GENITALIS 

 PENIS CLITORIS 



URACHUS 



INTERIOR OF BUDDER 



OPENINGS OF URETERS 



URETHRA 



OPENING OF MULLERIAN DUCT 



The earliest appearance is that of a tube called the Wolffian duct, which opens liy its hinder 

 extremity into a cloaca or common "'itlet lor the intestinal and urinary pa.-sages. From the fure 

 juirt of this duct is develojied a temj)orarj' organ, the pronephros, or head-kidney, in the iiiim 

 of vascular glomeruli. Bihind this soon a|)pear a nuud>er of tulK>. which open at riLiht 

 angles inti> the mid portion oi'the duet, and con.-titute the mesonephros, mid-kidney, or Wolffian 

 body. Still farther back, Irom the ]Mj:>teiior end of the duct, springs the metanephros, or hind- 

 kidney, a Hiesoblastic growth around a hollow branching iirotrusion trom the duct, with which 

 tubules and glomeruli subsiMpiently become connected, riie pronephros (|uickly di>apiiears in 

 the higher vertebrates: the niesonephros, which reaches its maximum development by the sixth 

 week, soon ceases to discharge its renal i'unction, and either becomes a u.sdess relic in the broad 

 ligament of the female nelvis, or tuidergoes transformatittn into an essential i)art oi' the male 

 generative apparatus ; wliile the metanephros becomes developed into the ])ernianent kidney. 

 The ureter and Jirinii'erous tubules i)robably originate as special outirrowths from the po.^terior 

 part of the Wolifian duet. The luorpliolotry of the suprarenal body is somewhat doubtiul. but it 

 is probable that the medulla is a derivative of the synnpathetie sy>tem. and hence of epiblastic 

 origin ; while the cortex is a me.sobla.stic development \n conne<;tion with the fore end of the 

 Wolffian duct. It is at first larger than the kidney, but the latter attains au equal bulk by the 



