Fig. 1. Evolution of the four a-es (mouth a-is [MA], pharyngeal a-is [PA], laryngeal a-is [LA], line of vision [LV]) and the α, β, and δ angles in the three head positions. The magnetic resonance images are shown for patient no. 5. (A ) Neutral position; (B ) simple head extension; (C ) “sniffing” position.