The relationship between the length of the cervical spinous processes and the inclination of the spines, the size of the vertebrae, the depth of the excavations on the superior aspect of the vertebral bodies, the inclination of the articular facets, the length of the nuchal plane and the size of the skull and the position of the head were studied in 270 specimens of different primate species. In addition the individual sexual ranges of variation of these measurements were determined. Certain conclusions on the factors affecting head balance and the specialization of man were drawn.