The effects of experimental unilateral anotia on skull development in the chick embryo. V. The development of the brain and its meningeal envelope in embryos of 9-20 days of incubation.

In a total number of 27 normal and 27 unilaterally anotic chick embryos, varying in age from 9-19 days, the morphogenetic relationships between the neurocranium on the one hand and the brain and its meningeal envelope on the other were studied. The results showed that, in general, unilateral anotia slightly interferes with the development of the bain. Only the homolateral nucleus tangentialis and cerebellar auricle proved to be underdeveloped. However, the brain of the anotic embryos progressively develops asymmetrically: In an antero-posterior and a ventro-dorsal direction abnormal flexures are present, and various components of the brain on the anotic side undergo changes in shape and position. These changes in brain morphology are interpreted as secondary features. Hence, the conclusion is drawn that the neurocranium, through the intermediary of the meningeal envelope, controls--or at least is capable to control--the general morphological development of the brain.