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The flexion of the cranial base and ontogenic migration of the foramen magnum in Macaca mulatta were investigated. Longitudinal cephalometric studies were carried out in infant and juvenile groups. Significant ontogenic changes of the cranial base were observed only in juvenile age group. The infant group did not exhibit any changes of the cranial base angle or migration of the foramen magnum. The diameter of the latter in infants exhibited small but statistically significant changes.

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.

Cross-sectional studies of the degree of the cranial base flexion were carried out in infant, juvenile and adult skulls in four genera of nonhuman primates (P. paniscus, H. lar, P. urinus, and M. mullatta). The cephalometric observations of the cranial base included linear and angular measurements of each specimen. The data obtained in this study showed that the anterior portion of the cranial base exhibits a significant shortening trend as the mammalian evolutionary scale ascends. Moreover, the growth pattern of the anterior portion of the skull base follows that of the facial bony structures. The ontogenic growth changes of the posterior portion of the skull base follows the growth pattern of the endocranial cavity. The significant trend of elongation in this area directly contributes to the posterior migration of the foramen magnum. The magnitude of these growth changes decreases as the evolutionary scale ascends. The angular measurements of the cranial flexion showed a less obtuse cranial base angle in young specimens and the ones higher on the mammalian scale. The skull kyphosis was less pronounced in these specimens and the anatomical features of the cranial base were more humanlike, including the balance of the head expressed by the position of the foramen magnum.

A spina-bifida-like condition was induced in 8 Macaca mulatta fetuses by intra-uterine lumbar laminectomy (L3-L5) followed by displacement of the spinal cord from the central canal. This condition was repaired in utero in 5 animals. A key feature of the repaired in utero in 5 animals. A key feature of the repair method was the use of allogeneic bone paste made from fetal bone particles suspended in an agar-thickened modified Dulbecco's medium. The bone paste was used to correct the bone deficit produced by the laminectomy. All of the monkey babies were delivered by cesarean section at near term (160-164 days of gestation). Neurological test on the neonates and subsequent morphological studies indicated that the in utero treated animals developed normally. In contrast, 3 control animals, which had the induced spinal dysraphism but were left untreated, showed severe spina-bifida-like abnormalities, including paraplegia, incontinence and somatosensory loss.