436 TEXT-BOOK OF EMBRYOLOGY. 



urethra and is known as uracho-vesical fistula. The urachus may degenerate 

 in part, leaving disconnected portions which frequently become dilated to 

 form cysts. 



Vesical fissure, the most serious malformation of the bladder, is associated 

 with fissure of the lower abdominal wall. The edges of the cleft in the bladder 

 are continuous with those of the cleft in abdominal wall, the integument being 

 continuous with the lining of the bladder. In some cases the bladder is 

 everted through the cleft, and the cleft may even be so extensive as to involve 

 the external and internal genital organs. Vesical fissure is much more com- 

 mon in the male than in the female. No very satisfactory explanation of this 

 malformation has yet been given. It is in some way connected with imperfect 

 formation of the ventral abdominal wall resulting from influences acting at a 

 very early period of development. 



THE URETHRA in both sexes may be abnormally small or abnormally large 

 or partly occluded, owing to faulty development of the urogenital sinus. In 

 the male the penile portion also may be malformed, being represented merely 

 by a furrow on the lower side of the penis. This condition, known as hypo- 

 spadias, is due to the incomplete fusion or lack of fusion between the genital folds 

 along the lower side of the genital tubercle (p. 428). In extreme cases the de- 

 fect may involve the scrotum and extend back as far as the prostate gland, the 

 two halves of the scrotum being separated. Epispadias, in which the urethral 

 cleft extends along the upper side of the penis (or the clitoris) is rare, and is 

 usually associated with vesico-abdominal fissure. Its mode of origin is not 

 understood. 



THE TESTICLES. One of the most common malformations affecting the 

 male genital glands is the condition known as chryptorchism, in which the 

 glands, instead of descending into the scrotum, are retained within the ab- 

 dominal cavity. One or both testicles may be affected. They may occupy 

 their original position far forward in the abdominal cavity or may be situated 

 near the inguinal canal, or may lie at some intermediate point. The malposi- 

 tion is due to a failure in the normal descent into the scrotum (p. 423). The 

 cause of the failure is obscure. Not infrequently the ectopic testicles atrophy 

 or fail to develop properly at puberty. 



Congenital absence of one or both testicles is rare. More frequently the 

 gland or efferent system of ducts is defective in part, owing to imperfect 

 development. In case of absence of the testicles the individual is small and 

 poorly developed; when the glands are imperfectly developed the individual is 

 effeminate. 



Cysts which are sometimes met with in the epididymis are possibly due to 

 dilatation of incompletely degenerated portions of the mesonephric tubules 

 or Miillerian ducts. Teratoid tumors and chorio-epitheliomata are occasionally 



