Fig. 6. Internal view through the trachea (a–f) and external view along the trachea (g–i) of the cockatiel syrinx illustrating the effects of electrical stimulation of the muscles shown in the insets to the right. (a,c,d,f) During quiet respiration, the cranially arching lateral tympaniform membranes (LTMs) of the cockatiel syrinx are positioned in the tracheal lumen, forming a dorso-ventral slot (S). (b) Stimulation of the right m. syringealis superficialis (SS) adducts the ipsilateral LTM (left in picture) into the middle of the tracheal lumen, narrowing S (yellow arrowheads). (e) Stimulation of the left m. syringealis profundus (SP) abducts the ipsilateral LTM (right in picture) from the tracheal lumen, widening S (yellow arrowheads). (g–i) The same situation viewed from the outside caudally along the tracheal axis (see inset). Stimulation of the left SP (h) abducts the ipsilateral member of the paired protrusions (PP) (red arrowheads) as it is drawn cranio-laterad. When stimulation is terminated, the left PP move back into the respiratory position (i). D, dorsal side; V, ventral side.
