Final answer:
The atlantoaxial joint involves the superior and inferior articulating processes of the axis and atlas, as well as a pivot joint between the dens and anterior arch. The proximal radioulnar joint involves the head of the radius and the radial notch of the ulna, held in place by a ligament.
Step-by-step explanation:
The joints involved in the atlantoaxial joint are the superior articulating processes of the axis which articulate with the inferior articulating processes of the atlas, as well as the pivot joint formed between the dens of the axis and the anterior arch of the atlas. On the other hand, the joints involved in the proximal radioulnar joint are the head of the radius which articulates with the radial notch of the ulna, and is held in place by a ligament.