THE UROGENITAL SYSTEM. 



119 



thus separated from the rectum by the ingrowth of two lateral 

 cloacal septa. 



septum 



cord. J 



allantois 



bladder- 



cord i^isi 



urogenit. sinus^ 

 genit tub. 



genit tub 

 perineal, dep. — . 

 cloacal. memb 



caudal end. 



■cloaca 



Wolffian duct. 



perineal sept 



septum' 



audal end 



B 



Fig. 95. — The Division of the Cloaca into Rectal and Uro-genital Parts. 



A. First appearance of the separation of tne Cloaca into Rectal and Uro-genital 



Parts (3rd week). 



B. Separation of the Cloaca into Rectal and Uro-genital Parts (5th week). 



The Proctodaeum or Primitive Perineal Depression. — 



Although the main part of the perineal body is formed in the 

 manner just described, a second element, which forms the surface 

 part of the perineal body is formed thus : 



Between the caudal protuberance behind, and the genital tubercle 

 in front (Fig. 95i?), the epiblast dips in as a median depression 

 to form the proctodaeum or primitive perineal depression. The 

 depressed area comes in contact with the ventral surface of the 

 cloaca (Fig. 95^4). By the ingrowth of a perineal septum from 

 each lateral margin of the depression, the proctodaeum is sepa- 

 rated into a posterior or anal part, and an anterior or uro-genital part. 



