4 AUGUSTUS G. POHLMAN 



downgrowth. Lieberkiihn ('82) and Keibel ('89) dispute the 

 theory of Rathkc ('32) championed bj' von Mihlacovics ('85), 

 that the bladder arises from the allantois, and state that it is made 

 up for the most part from the ventral cloacal segment — agreed 

 to by Retterer and Reichel. Born takes a neutral position and 

 believes that at least the trigone of the human bladder may be 

 developed in a manner like that found in the guinea pig (Keibel) . 

 Born and Minot do not think that the anlage of the upper part 

 of the bladder is of particular importance. "We are probably 

 not mistaken when we grant that not only the bladder (as far 

 as the apex) but the male urethra as far as the caput gallinaginis, 

 the entire female urethra, and in the male, also the pars prostatica 

 and the entire pars membranacea are developed from the ventral 

 cloacal segment." 



The most important of the recent works is that of Ke bel ('96) 

 who sums up the development of the cloacal region in the following 

 words : '' The human embryo possesses a large entodermal cloaca 

 in the early stages of its development which however is never 

 opened to the outside through a cloacal anus ('Cloakenafter' 

 of Prenant), but remains closed through the cloacal membrane 

 (the 'anal membrane' of the earlier writers) as long as it exists 

 as such. An ectodermal cloaca is to be found only in traces if at 

 all. The entodermal cloaca is separated into a ventral and a dor- 

 sal segment by a frontal septum. A large part or all of the bladder, 

 the urethra and the urogenital sinus as far as the cloacal membrane 

 are derived from the ventral segment; while the dorsal segment 

 beconjes continuous with the ectodermal segment of the rectal 

 canal. The primitive perineum is formed when the frontal sep- 

 tum fuses with the cloacal membrane and the rudimentary ecto- 

 dermal cloaca is then divided by the permanent perineum. The 

 ectodermal anal pit (protodaeum) is situated behind the perma- 

 nent perineum, while the ectodermal portion of the urogenital 

 sinus is ventral to it." 



Another investigator, who has been particularly fortunate in 

 the amount of embryological material at his disposal, expresses 

 a somewhat different view. Nagel ('02) practicall}- reiterates 

 his statements of 1894. "The inspection of the tail end of human 



