Hydrops amnii, also known as hydramnion, or hydramnios, is a term taken from medical terminology where in the female the allantois ceases to exist at an early date and the dropsy naturally occurs in the amnion. In veterinary obstetrics this term is somewhat of a misnomer since in domestic animals there exists two ample cavities of the fetal envelops, the amniotic and allantoic, which regularly contains fluids in varying amounts. In veterinary obstetrics the term is used to indicate an excessive amount of fluid in the allantoic or the amniotic cavities. These two cavities communicate through the urethra-urinary bladder-urachus passageway and approximately equal pressure is maintained within the two cavities. The allantoic sac is much larger and generally contains the major volume of the fluid.