Causes In The Foetus itself are mainly of two kinds, namely, want of energy in the formative powers, and disease in the foetus, chiefly dropsy, calculated to interfere with the closure in the middle line of the neural or ventral arches. It is difficult to assign their due places to each of these causes. In the case of defect in the cerebro-spinal canal, there are cases of extreme defect of the neural arches, including nerve structures, bones, and integuments as to suggest a primary defect in the formative power. On the other hand over-distension of the closed neural canal (ultimately represented by the ventricles of the brain and the central canal of the spinal cord) by fluid, constituting a dropsy, is not uncommon, and if it occur early it may interfere with the closure of the enveloping structures, the bones - and soft parts. Again, the dropsy may be such as to lead to rupture of the canal, in which case there will be a secondary incompleteness of the neural canal, as well as of the enveloping structures. Opinions differ as to the part taken on the one hand by imperfect formative power, and on the other by dropsy and rupture in the production of these malformations.

In regard to the ventral arches the question of causation in the foetus itself is "also obscure. Dropsy does not seem so frequent here, but rupture of the allantois from dropsy is probably the cause of defects in the closure of the abdomen below the umbilicus.