The more considerable of these have been considered in the section on general malformations. The principal forms are anencephalus accompanied by acrania or cranioschisis, encephalocele and cyclopia. The relation of these to dropsy of the ventricles of the brain (hydrocephalus) has also been considered. It has been pointed out that hydrocephalus occurring at an early period leads to these serious malformations, which are incompatible with life. But hydrocephalus sometimes occurs at a later period, and the child is born with, a congenital hydrocephalus, which is itself sometimes regarded as a malformation. It will be taken up, however, along with the other forms of hydrocephalus.