862 DEVELOPMENT. [CH. LVIII. 



and Miillerian ducts, open into a receptacle formed by the lower 

 end of the allantois, or rudimentary bladder ; and as this com- 

 municates with the lower extremity of the intestine, there is for 

 the time a common receptacle or cloaca for all these parts, which 

 opens to the exterior of the body through a part corresponding 

 with the future anus, an arrangement which is permanent in 

 reptiles, birds, and some of the lower mammalia. In the human 

 foetus, however, the intestinal portion of the cloaca is cut off 

 from that which belongs to the urinary and generative organs ; a 

 separate passage or canal to the exterior of the body, belonging 

 to these parts, is called the sinus uro-genitalis. Subsequently, 

 this canal is divided, by a process of division extending from 

 before backwards or from above downwards, into a ' pars urinaria ' 

 and a ' pars genitalis.' The former, continuous with the urachus, 

 is converted into the urinary bladder. 



The external parts of generation are at first the same in both 

 sexes. , 



The opening of the genito-urinary apparatus is, in both sexes, 

 bounded by two folds of skin, whilst in front of it there is 

 formed a penis-like body surmounted by the glans, with a cleft or 

 furrow along its under surface. The borders of the furrows 

 diverge posteriorly, running at the sides of the genito-urinary 

 orifice internally to the cutaneous folds just mentioned. In the 

 female, this body becoming retracted, forms the clitoris, and 

 the margins of the furrow on its under surface are converted 

 into the nymphse, or labiae minora, the labia majora pudendse 

 being constituted by the great cutaneous folds. In the male 

 foetus, the margins of the furrow at the under surface of the 

 penis unite at about the fourteenth week, and form that part of 

 the urethra which is included in the penis. The large cutaneous 

 folds form the scrotum, and later (in the eighth month of develop- 

 ment), receive the testicles, which descend into them from the 

 abdominal cavity. Sometimes the urethra is not closed, and the 

 deformity called hypospadias then results. The appearance of 

 hermaphroditism may, in these cases, be increased by the reten- 

 tion of the testes within the abdomen. 



The supra-renal capsules originate in a mass of mesoblast just 

 above the kidneys ; soon after their first appearance they are very 

 much larger than the kidneys (see fig. 68 1), but by the more 

 rapid growth of the latter this relation is soon reversed (see also- 

 P- 335)- 



