anatomical axis proximal-distal axis An axis that extends from the point of attachment of a structure (proximal) to the point furthest away from the plane of attachment (distal). BSPO:0000015 In some communities, proximal and distal are used when specifying the position of parts of elements that are contained within the body, such as gill arches or vertebral spines. In these cases, use of the classes medial-lateral axis or medial-external axis are more appropriate. proximal/distal proximodistal spatial