THE UKO-GENITAL SYSTEM. 



123 



to form the urethral floor, the erectile tissue contained in them, 

 corresponding to the bulbs of the vestibule of the female, also 

 fuses and thus the corpus spongiosum is formed. The part 

 of the urethra within the glans is the last part to be formed, 

 and its development is peculiar. It is formed by a solid rod- 

 like ingrowth of epiblast within the glans which burrows back- 

 wards until it reaches the part formed out of the uro-genital 

 cleft. The glans part of the urethra becomes canaliculized a 

 short time before birth. The fossa navicularis and lacuna magna 

 occur at the junction of the part of the urethra formed in the 

 glans and the part formed by the union of the inner genital folds. 

 The closure of the uro-genital lips to form the floor of 

 the urethra in the penis may be arrested at any stage, 



,oblit. in cord 



V- urachus(allantois) 



bladder (cloaca) 



■j i upper prostatic 

 [from cloaca 



ejac. duct 

 (from Wolffian duct) 



j lower prostatic from 

 I urogen. sinus 



"memb. from urogen sinus 



from genital furrow and 

 urogenit. sinus 



ingrowth of epiblast 



Fig. 99.— A section of the male bladder and urethra at birth, showing the structures 

 derived from the intra-abdominal part of the Allantois and from the Cloaca. 



giving rise to the condition of hypospadias, a condition 

 normal in the female. It is not very rare to find the terminal 

 half inch of the urethra in a hypospadiac condition. If the 



