Growth control of neurocranial height of the rat skull.

In the present study the skulls of 36 experimentally bipedal adult male rats are compared with those of 47 adult male control rats, with particular attention to the relation length, width and height respectively of the neurocranium to brain size. It was shown that, on average, the neurocranium of bipedal rats was reduced in length and increased in height, while its width was unchanged. With respect to brain size the 2 groups were similar. It is postulated that the increase of height might be considered as a compensation for the loss of space due to the decreased length. The neurocranial height is the dimension in which adaptation to the space demands of the brain is realised. These adaptations are, therefore, controlled by a local epigenetic factor, viz. brain size.