Axis (anatomy) The condition, where the dens is separated from the body of the axis, is called os odontoideum, and may cause nerve and circulation compression syndrome. On its anterior surface is an oval or nearly circular facet for articulation with that on the anterior arch of the atlas. On the back of the neck, and frequently extending on to its lateral surfaces, is a shallow groove for the transverse atlantal ligament which retains the process in position. The apex is pointed, and gives attachment to the apical odontoid ligament; below the apex the process is somewhat enlarged, and presents on either
Neoteny in humans skull, thinness of the skull bones, lack of brow ridges, lack of sagittal crests, form of the teeth, relative size of the brain and form of the brain as ways in which the juvenile skulls of these human ancestors resemble the skulls of adult modern humans. Montagu said that the retention of these juvenile characteristics of the skull into adulthood by australopithecine or pithecanthropine could have been a way that a modern type of human could have evolved earlier than what actually happened in human evolution. The psychiatrist Stanley Greenspan and Stuart G. Shanker proposed a theory in "The First