622 



DEVELOPMENT. 



[CHAP. XLIIT. 



converted into the ureters. The ureters and urinary bladder are 

 gradually drawn into the cavity of the pelvis, through the umbilical 

 opening. This process, according to Langenbeck, is completed 

 between the twelfth and twentieth week. The urachus, between 

 the bladder and umbilicus, remains tubular long after this, and 

 even at birth in some few instances; in which cases urine has 

 been known to escape from the umbilicus. 



Allantoic Fluid is clear, of a brownish -yellow colour. Its specific 



gravity varies from 1005 to 1030. It contains alkaline lactates, 



Fig. -293. extractive matters, 



and ammoniacal 

 salts, with alkaline 

 and earthy phos- 

 phates, and chlo- 

 ride of sodium, Be- 

 sides these, however, 

 there is a definite 

 crystallizable sub- 

 stance peculiar to 

 this fluid, termed 

 allantoin, which is 

 closely related to 

 uric acid ; indeed, 

 it may be prepared 

 artificially from this 

 substance, while urea 

 is produced at the 

 same time. The 

 composition of al- 

 lantoic fluid seems 

 nearly identical wit] 

 that of the urine 

 calves while suck- 

 ling, at which time 

 it contains no hip- 



Diagram of uterus, with a fully formed, but very young ovum.- 1. r>uric acid. This 

 ug of mucus occupying cervix uteri. 2. Opening of Fallopian tube, j 



latter substance, 

 however, makes its 

 appearance in the 



urine as soon as the animal takes vegetable food. Uric acid hj 

 been found in the allantoic fluid of birds, by Jacobson. 



Velpeau held that the allantois completely surrounded the hum: 



Plug of mucus occupying cervix _ 

 3 Deciduavera. 4. Cavity of uterus, nearly filled with ovum. 5. De- 

 cidua reflexa. 6. Chorion. 7. Decidua serotina. 8. Allantois in situa- 

 tion of placenta. 9. Amnion. 10. Umbilical vesicle. 11. Umbilical 

 cord. 12. Space between chorion and amnion, filled with albuminous 

 matter. 



