THE CLOACA IN HUMAN EMBRYOS 5 



embryos of 11-13 mm. length reveals an oval pit extending from 

 the coccygeal prominence to the tip of the genital eminence. 

 This pit (cloaca) receives the openings of the gut dorsally, and the 

 Canalis urogenitalis ventrally; the two separated by a partition 

 of some 0.3 mm. thickness. The Wolffian and Miillerian ducts 

 open higher up in the Canalis urogenitalis and will not be con- 

 sidered in the description of this depression. The Canalis uro- 

 genitalis and the gut open into this pit (cloaca) which would reach 

 (comparing with adult relations) from the dorsal border of the 

 anus to the ventral border of the urethral opening {i.e. Frenulum 

 clitoridis). Later he states: ''In what manner the division of 

 the cloaca is accomplished is not perfectly understood either in 

 man or in mammals. I found the relations in the j^oungest human 



Fig. 1 



embryo that I had opportunity to examine like those pictured 

 in fig, 1, naturally with exception of the form of the bladder. 

 I commit myself therefore, as far as the human embryo is con- 

 cerned, to the view of Rathke which has recently been substan- 

 tiated by Retterer and von Mihalcovics in the animals." 



The work of von Mihalcovics i/85) referred to, says in part; 

 ''This septum between the urogenita' canal and the gut arises 

 in part through increase in length of the afore-mentioned perineal 

 Told (septum) to which, distalward, two lateral folds join to the 

 perineal folds. The cloaca takes no part in the formation of the 

 urogenital canal. "The opinion of Retterer ('94), mentioned by 

 Nagel, is summarized as follows: "In the guinea pig, as in other 

 mammals studied up to the present time (man, pig, sheep and rab- 



