An AP axial cranial projection (Towne method) with accurate positioning demonstrates

1. equal distances from the posterior clinoid processes to the lateral borders of the foramen mag-num on each side.
2. the midsagittal plane perpendicular to the IR.
3. the dorsum sellae within the foramen magnum.
4. the posterior clinoids inferior to the foramen magnum.

a. 1, 2, and 3 only
b. 1 and 3 only
c. 2 and 4 only
d. 1, 2, 3, and 4

Answer is a. 1, 2, and 3 only