Chamberlain line
Chamberlain line is a line joining the back of hard palate with the opisthion on a lateral view of the craniocervical junction.
Significance
It helps to recognize basilar invagination which is said to be present if the tip of the dens is >3 mm above this line.
McGregor developed a modification of the Chamberlain line for when the opisthion could not be identified on plain radiographs.