Relationship between growth of brain and skull of Macaca mulatta and its importance for the stereotaxic technique.

An analysis of the brain weight of 196 rhesus monkeys and lateral X-rays of 91 more was made to determine and correct the effect of growth and development on sterotaxic variability. A comparison of body weight to brain weight shows that the brain grows rapidly initially in a linear relationship with body weight and can increase in weight even into adulthood, with a significant amount of variability found throughout its development. The examination of the cranial base and sterotaxic reference points indicates that the brain rotates during growth in a forward and downward direction in relation to the sterotaxic planes. The distance between the anterior clinoid process and AP-0 shows an increase of little variability from linearity during growth. This distance can be used to correct for the anterior-posterior plane found in standard stereotaxic atlases. The flattening out of the cranial base results in a horizontal plane readjustment during growth. A horizontal correction can be made by measuring the distance between the base of the pituitary fossa and H-10 plane.