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An experimental study of functional and adaptive growth changes of the gonial region associated with removal of all anterior teeth is being carried out through the life span of the Macaca mulatta monkeys. Radiographic cephalometry, using metallic implants as consistent points of reference and histological methods using in vivo tetracycline bone labeling, are the principal experimental techniques in the study. The present paper covers the results obtained from the longitudinal observations of the infant group from two to 24 months of age. The angular measurements of the gonial angle, linear measurements of the horizontal and vertical rates of growth in the gonial region were made in experimental and control groups. The data obtained from the angular measurements showed negative regression trends in both groups. The data from linear measurements of horizontal and vertical rate of growth exhibited positive linear regression trends with age. The histological findings, however, indicate differences between the two groups. Sections from the control group show some bone apposition in the gonial region, while experimental animals show extensive resorption. The results of this study show the inadequacy of standard anthropometric methods in the determination of adaptive growth changes of the gonial region at that early age.

The contribution of the basicranial synchondroses in the growth of neurocranial length and ontogenetic development of the cranial base were investigated. The study concentrated on the midsphenoidal synchondrosis and its delayed fusion in nonhuman primates when compared to man, and on the spheno-occipital synchondrosis. The mode and time of fusion of both growth centers were observed, and their role in the ontogenetic growth changes (flattening processes) of the cranial base were established. The chondrogenic ossification of midsphenoidal and spheno-occipital synchondroses was studied on 20 skulls of Macaca mulatta females, ranging in age from newborn specimens to those 24 months old. The technique of in vivo tetracycline bone labeling was used for histologic evaluation of the material. Different chondrogenic growth patterns were observed in both synchondroses. The endochondral activity of the spheno-occipital synchondrosis increased with age, from a nonactive narrow cartilaginous column in the neonatal specimen to a broad band with high chondrogenic ossification in the 24-month-old specimens. This growth center contributes to elongation of the posterior portion of the cranial base and is a secondary factor in its flexion. The midsphenoidal synchondrosis seems to be the primary factor in the mode of flexure of the cranial base in Macaques. This growth center is very active in the first ten months of life but later exhibits cessation of chondrogenic activity and long remains unfused. The first signs of fusion were observed as late as 72 months of age. At the same time, the continuous process of cranial base flattening showed the first signs of tapering off.