X-ray localization of limbic structures in the cynomolgus monkey (Macaca fascicularis)

The anterior/posterior (AP) and dorsal/ventral positions of 3 subcortical structures, the amygdala, the mamillary bodies, and the anterior commissure, were estimated with respect to the skull in a series of cynomolgus monkeys (Macaca fascicularis). The distance from the external auditory meatus, from which stereotaxic coordinates are typically derived, to these structures was found to be highly variable. In contrast, radiography revealed that a skull landmark which forms part of the sphenoid bone lies at a remarkably constant distance from these 3 structures. The posterior clinoid process also proved to be a more accurate reference point than the auditory meatus, although it was less reliable than the sphenoid landmark. It is proposed that the position of the sphenoid bone could be used to localize a wide range of limbic and basal forebrain structures.