Figure 1: Morphology associated with Polypterus spiracular air breathing.

(a,b) Sagittal and transverse magnetic resonance images of P. palmas showing the path (arrows) of air through the spiracles to the buccopharyngeal chamber and lungs. (c) Dorsal view of the head of P. bichir showing the position of the two dermal ossicles (Sp1, Sp2) that form the spiracular valve (Sp). (d) P. delhezi with the spiracular valves open and emerged during aspiration. Dhy, dermohyal; Esc, extrascapular bone; Fr, frontal; Int, Intertemporosupratemporal bone; N, nasal; Op, opercle; Pop, preopercle; Sop, subopercle. Non-spiracular ossicles are labelled with numbers: prespiracular ossicles (1–5), post-spiracular ossicles (8–10).