Most of the studies on pressures within the craniovertebral cavity have been conducted on adult human beings or on full-grown animals. Obviously, the adult cranium and spinal column are relatively fixed in shape and in capacity and can probably be considered as a closed box completely filled with various soft or fluid substances to which the rules of physics concerning the transmission of pressure where fluids completely fill rigid, communicating containers will apply.
We do not propose to challenge the approximate accuracy of such a conception of transmission of pressure in adults, but we feel that the rigid box idea is unsound in theory and in fact frequently invalid in the human infant. In the first place, under every-day stresses the skull and the spinal column of the infant are subject to expansion, contraction and distortion to a degree which makes any such phrase as "closed box of constant volume"