THE UKO-GENITAL SYSTEM. 



125 



(3) The uro-genital sinus or canal, and the parts derived from 

 it which have been already described (Fig. 93 and page 115). 



(4) The terminal part of the rectum. 



Ectopia vesicae is as yet unexplained. The condition is shown 

 diagrammatically in Fig. 100 A. This condition appears to be 

 produced thus : 



(1) The development of the tail in the embryo thrusts the 

 region of the primitive streak, situated on the body-stalk, 

 towards the ventral aspect of the body. The uro-genital part 

 of the perineal depression and the cleft into the uro-genital 

 sinus are formed in the line of the primitive streak (Fig. 158, 

 p. 192). The body-stalk which at first is a direct continua- 

 tion of the body (Fig. 75, p. 96), is arrested in its migration 

 towards the ventral surface of the body. It is arrested 

 between the rami of the pubes, and prevents the formation 

 of the symphysis. 



umbilic. 



belly wall 



post, wall bladder 



ureter 



ii±—ejac. ducts 



Wolff an duct 



B. 



Pig. 100.— A A section to show the condition of parts in Ectopia Vesicae. 



B. Section of the pelvis of an embryo (4th week) to show how the condition 

 is probably produced. 



(2) The uro-genital cleft is formed in front of and above the 

 genital tubercle instead of below it. The cleft opens thus into 

 the anterior Wall of the bladder instead, as it normally does, into 

 the uro-genital sinus (Fig. 100 5). 



It is also possible that the condition of ectopia vesicae is due 

 to a dropsical condition of the allantois, with subsequent rupture, 

 in the embryonic condition. 



