Fig. 1. Schematic explanation of dynamic configurational changes during direct laryngoscopy procedures with simple neck extension (b, c ) and the sniffing position (d–f ). (a ) Original structural configuration, (b ) neck extension on the flat table, (c ) laryngoscopy, (d ) placing a pillow, (e ) slight extension of the plane of the face, (f ) laryngoscopy. A = obstacles located anterior to the oral airway space (tongue, epiglottis, mandible, and others); P = obstacles located posterior to the oral airway space (upper teeth, maxilla, head, and others); VC = vocal cords. Shaded area represents visual field.