The mechanism of breathing in the South Asmerican lungfish, Lepidosiren paradoxa; radiological study

In filling the lungs by means of the buccal "force-pump", air drawn into the buccal cavity by the lowering of the floor of the mouth is forced into the lungs when the mouth is firmly closed and the buccal floor raised. This mechanism depends on the ability of the fish to prevent air being forced out of the mouth through the lips and it is shown that the tongue is pressed against the roof of the mouth to form a seal. Radiologically it has been shown that the hyoid apparatus ("ceratohyal" of some authors) plays a large part in the movements necessary to draw air into the mouth, seal it in and force it into the lungs. Another skeletal element involved is the pectoral girdle which makes considerable movements in association with the filling of the lungs. Expiration of the air from the lungs, which as shown by radiographs may be remarkably complete, is brought about by the elasticity of the lung tissue.